The following systematic descriptions and discussion include only a portion of the Mesozoic species found during this study. Taxa not cited in Appendix A appear in Appendix B.
Size ranges are as observed in this study with the holotype measurement indicated in parentheses. Photographic negatives are used as types, and film and frame numbers cited herein are stored at the Department of Geology of the Florida State University (FSU). Holotype micrograph numbers are given in the plate captions.
Genus ANSULASPHAERA Grün and Zweili, 1980
Ansulasphaera covingtonii sp. nov.
(Pl. 1. Figs. 1-18)
Diagnosis. A small- to medium-sized, circular to elliptical species of Ansulasphaera with a distally extended element cycle.
Description. The circular to elliptical placolith is constructed of three shields. A narrow distal shield is constructed of a single cycle of vertical to subvertical elements. The broad, subhorizontal median shield is constructed of imbricated elements having nonradial sutures. The proximal shield is formed by a single cycle of subvertical, blocky elements. The distal shield height is approximately one-third of the proximal shield height. The central area is open.
In cross-polarized light, this species is easily distinguished in lateral view. In plan view, both the proximal and distal cycles exhibit a first-order white birefringence, whereas the median cycle is faintly birefringent to dark. The proximal element cycle can be distinguished from the distal element cycle by its greater thickness and height.
Size. 4.0 to 6.0 (holotype: 4.6 µm).
Remarks. Ansulasphaera covingtonii differs from Ansulasphaera helvetica by its distally extended element cycle and younger stratigraphic occurrence. A. covingtonii is described herein from the Tithonian and may range into the Cretaceous, whereas A. helvetica is not known to have survived the Callovian.
Derivation of name. In honor of the nannofossil paleontologist James Mitchener Covington.
Holotype. Plate 1, Figures 4-8, specimen transferred from the LM to the SEM.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian.
Occurrence. Rare to common in Tithonian sediments from ODP Hole 901A.
Genus AXOPODORHABDUS Wind and Wise in Wise and Wind, 1977
Axopodorhabdus cylindratus (Noël, 1965) Wind and Wise in Wise and Wind, 1977
(Pl. 11, Figs. 3, 10, 11)
Axopodorhabdus rahla (Noël, 1965) Grün and Zweili, 1980
(Pl. 11, Figs. 14, 15)
Genus BISCUTUM Black 1959 emended de Kaenel and Bergen, 1993
Biscutum rotatorium (Bukry, 1969) comb. nov.
Bidiscus rotatorius Bukry, 1969, p. 27, pl. 27, figs. 5-9.
Discorhabdus rotatorius (Bukry, 1969) Thierstein, 1973, p. 42, pl. 5, figs. 13-16.
Remarks. This species is transferred into the genus Biscutum based on its rim construction (i.e., two subhorizontal, unicyclic shields). The central area is imperforate. In cross-polarized light, the distal and proximal shields exhibit a faint birefringence. The central area elements are birefringent.
Genus BRAARUDOSPHAERA Deflandre, 1947
Braarudosphaera regularis Black, 1973
(Pl. 11, Figs. 26, 27)
Genus CALCIVASCULARIS Wiegand, 1984
Calcivascularis sp. 1
(Pl. 6, Figs. 17, 18)
Remarks. This small form of Calcivascularis has two sub-parallel walls and a circular horizontal outline. The central portion is filled by cycles of radial elements. This form is present in Kimmeridgian strata in Portugal, southeastern France, and at DSDP Site 534.
This form is distinguished from Calcivascularis jansae Wiegand, 1984 by its small size, continuous central core (in lateral view), and higher number of rim elements.
Genus CHIASTOZYGUS Gartner, 1968
Chiastozygus leptostaurus Cooper, 1987
(Pl. 10, Figs. 13, 14)
Genus CLEPSILITHUS Crux, 1987
Clepsilithus meniscus sp. nov.
(Pl. 7, Figs. 6, 14-16)
Diagnosis. A very small species of Clepsilithus with a narrow rim.
Description. A very small, elliptical murolith with a narrow rim. The low distal shield is constructed of imbricated elements. Numerous, somewhat radial elements fused into a central plate extend from the reduced proximal shield toward the center of the coccolith, but leave a small central opening. The rim extinction pattern is unicyclic and weakly birefringent, whereas the central plate is more birefringent.
Size. 2.5 to 3.5 µm (holotype: 3.0 µm).
Differentiation. The appearance of a fused central plate composed of thickened, radial bars may be a preservational artifact. The elliptical outline, central opening, and disposition of these central bars conforms to Clepsilithus Crux, 1987. It is distinguished from Clepsilithus polystreptus by its narrow rim and central plate.
Derivation of name. From Greek, meniskos: crescent.
Holotype. Plate 7, Figures 6, 14-16; specimen transferred from the LM to the SEM.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian.
Occurrence. Rare in lower Tithonian sediments from ODP Hole 901 A.
Genus CONUSPHAERA Trejo, 1969
Conusphaera mexicana Trejo, 1969 subsp. minor Bralower 1989
(Pl. 4, Figs. 1-12, 15-17; Pl. 5, Figs. 4, 10;
Pl. 6, Figs. 1, 2, 4, 5, 7-13)
Conusphaera mexicana Trejo, 1969 subsp. minor Bralower ex Bown and Cooper, 1989b; in Bralower, Monechi, and Thierstein, 1989, p. 223, 225, 228, pl. 7, figs. 21-25.
Remarks. Rare forms of Conusphaera mexicana ssp. minor have an extended wall or a low inner core (Pl. 4, Figs. 1, 4; Pl. 5, Figs. 4, 10). These specimens are gradational between Conusphaera sinespina (elliptical, no inner core) and more typical C. mexicana ssp. minor (elevated inner core). C. mexicana may have evolved from an elliptical murolith with a nonimbricated wall, such as Stradnerlithus. Many specimens of C. mexicana ssp. minor possess an elliptical to subelliptical shape (Pl. 4, Figs. 13, 14). C. mexicana ssp. minor is subdivided in this study according to the nannolith shape in plan view (perpendicular to the longitudinal axis) and indicated as C. mexicana minor (circular) and C. mexicana minor (elliptical) in the Table 2. The abundance of specimens with elliptical or circular apical outline is indicated in Table 2. Both nannolith shapes are present in most nannofossil assemblages. Elliptical specimens are as abundant as circular ones.
Rare detached spines of C. mexicana ssp. minor were also observed (Pl. 5, Figs 11-17). In cross-polarized light, these forms are similar to small Polycostella beckmannii. A specimen transferred during the current study (Plate 5, Figs. 11, 12, 17) show similarities to the holotype of Polycostella beckmannii Thierstein, 1971 (pl. 2, fig. 6). Therefore, it is possible that Polycostella beckmannii and Conusphaera mexicana are related or possibly synonymous. Additional upper Tithonian specimens must be transferred to clarify this potential taxonomic problem.
Conusphaera mexicana Trejo, 1969 ssp. mexicana (Bralower, 1989)
(Pl. 6, Figs. 3, 6, 14-16)
Conusphaera mexicana Trejo, 1969, p. 6, pl. 1, figs. 1-5; pl. 2, figs. 208, pl. 3, figs. 1-7; pl. 4, figs. 1-4.
Conusphaera mexicana Trejo, 1969 subsp. mexicana Bralower; in Bralower, Monechi, and Thierstein, 1989, p. 228, pl. 7, figs. 16-20.
Remarks. The autonym was fixed by the description of Conusphaera mexicana ssp. minor by Bralower (in Bralower, Monechi, and Thierstein, 1989). Conusphaera mexicana ssp. mexicana is distinguished by its greater size and height/width ratio.
Conusphaera sinespina sp. nov.
(Pl. 5, Figs. 1-3, 5-9)
Diagnosis. A species of Conusphaera with an elliptical horizontal peripheral outline, a low shield, and no central spine (or core).
Description. A truncated, conical murolith with an elliptical, horizontal peripheral outline. The low distal shield is formed by a single cycle of 18 to 24 vertical elements, which are oriented with their broad faces tangential to the horizontal periphery. A subhorizontal, proximal element cycle closes the central area; it is constructed of 14 to 16 helical elements that are twisted clockwise (in proximal view).
In plan view, the rim is faintly birefringent and the central, proximal elements are slightly birefringent to dark.
Size. 3.0 to 4.0 pm (holotype: 3.4 µm)
Differentiation. Conusphaera sinespina differs from Conusphaera mexicana by its distinct elliptical outline and the absence of an inner central core. In plan view and in cross-polarized light, the central area of Conusphaera sinespina exhibits a faint birefringent. The central core of Conusphaera mexicana exhibits a first-order white birefringence.
Derivation of name. From Latin, sine, without, and spina, spine.
Holotype. Plate 5, Figures 3, 9.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian
Occurrence. Rare in Tithonian of ODP Hole 901 A.
Gems CREPIDOLITHUS Noël, 1965
Crepidolithus parvulus sp. nov.
(Pl. 7, Figs. 2, 3, 5, 9-13)
Diagnosis. A very small species of Crepidolithus with a broad rim and a small central opening spanned by a thin plate.
Description. A very small, elliptical murolith with a broad, thick distal shield constructed of 20-24 lath-shaped, imbricated elements. A thin proximal plate fills the central area, but is easily damaged because of its delicate nature. A distal projection is not present.
The rim is faintly birefringent and the central plate is dark in cross-polarized light.
Size. 2.5 to 3.5 µm (holotype: 2.8 µm)
Differentiation. Crepidolithus parvulus differs from other Crepidolithus by its extremely small size and younger stratigraphic occurrence.
Derivation of name. From Latin, parvulus: little.
Holotype. Plate 7, Figures 2, 5, 9, 10; specimen transferred from the LM to the SEM.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian
Occurrence. Rare to few in Tithonian sediments from ODP Hole 901 A.
Genus CRETARHABDUS Bramlette and Martini, 1964
Cretarhabdus conicus Bramlette and Martini, 1964
(Pl. 8, Figs. 24, 25)
Genus CYCLAGELOSPHAERA Noël, 1965
Cyclagelosphaera deflandrei Manivit, 1966
Remarks. One morphotype (A) of Cyclagelosphaera deflandrei exhibits a yellow birefringence and is identified by its small, circular to subelliptical central area. Although rare in Tithonian sediments from Hole 901 A, this morphotype is more abundant and occurs more consistently than the second morphotype (B). The latter exhibits first-order yellow to red birefringence color and is identified by its large, elliptical central area This form is very rare in Tithonian sediments from Hole 901 A.
Genus DIADORHOMBUS Worsley, 1971
Diadorhombus scutulatus (Medd, 1971)
Medd, 1979
(Pl. 9, Figs. 12, 13)
Genus DIAZOMATOLITHUS Noël, 1965
Diazomatolithus galicianus sp.
nov.
(Pl. 2, Figs. 1-8; Pl. 3, Figs.
1,2)
Diagnosis. A small- to medium-sized species of Diazomatolithus possessing a narrow rim and bicyclic distal shield.
Description. The circular placolith is composed of two narrow shields of equal width. The distal shield is bicyclic. Its inner cycle is formed of steeply inclined, radial elements. The slightly broader outer distal cycle is constructed of subhorizontal elements with subradial sutures. The unicyclic proximal shield is constructed of slightly imbricated elements showing some proximal extension. The two shields form an angle of about 50°. The central area is open.
Size. 4.0 to 5.5 µm (holotype: 4.3 μm).
Remarks. Diazomatolithus galicianus differs from Diazomatolithus lehmanii by having a narrower rim composed by two equal-sized shields and a distinct inner distal cycle. Diazomatolithus shows its closest morphologic affinities to Ansulasphaera.
Derivation of name. After the Galicia Margin, off the coast of Portugal.
Holotype. Plate 2, Figures 1, 2, 4, 5; specimen transferred from the LM to the SEM.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian
Occurrence. Present to few in Tithonian sediments from ODP Hole 901 A.
Diazomatolithus lehmanii Noël, 1965
(Pl. 2, Figs. 9-11; Pl. 3, Figs.
3-8)
Diazomatolithus lehmanii Noël, 1965 (partim), p. 96, pl. 6, figs. 6(?), 8, 9(?), text fig. 26 (non pl. 6, figs. 7, 10; text figs. 25, 27).
Remarks. The problems with the identification of this species result from the composite of forms illustrated as this species by Noël (1965). These specimens belong to the genus Triscutum (Noël, 1965, side view, pl. 6, figs. 7, 10; text fig 25) and possibly specimens of Discorhabdus with missing or broken stems (Noël, 1965, pl. 6, figs. 6, 9). Specimens illustrated herein include both a transferred specimen (Pl. 3, Figs. 3-6), as well as a rotated specimen (Pl. 3, Figs. 7, 8) that is nearly identical to the holotype (Noël 1965, pi. 6, fig. 8).
The holotype and specimens illustrated herein characterize Diazomatolithus lehmanii as a circular placolith constructed of two relatively broad shields. Elements of both shields are slightly imbricated and surround a large central opening. The proximal shield (orientation is given from the curvature in Pl. 3, Fig. 6) is slightly broader, more steeply inclined, and its elements more strongly curved than the subhorizontal distal shield. A narrow distal wall is also visible (Pl. 3, Figs. 7, 8).
Genus DUPLEXIPODORHABDUS Varol and Girgis, 1994
Duplexipodorhabdus plethotretus (Wind and
Cepeck, 1979) Varol and Girgis, 1994
(Pl. 11, Figs. 16, 18)
Genus ETHMORHABDUS Noël, 1965
Ethmorhabdus gallicus Noël, 1965
(Pl. 11, Figs. 22, 23)
Ethmorhabdus hauterivianus (Black, 1971) Applegate, Covington, and Wise in Covington and Wise, 1987
(Pl. 11, Figs. 24, 25)
Ethmorhabdus rimosus Grün and
Zweili, 1980
(Pl. 11, Figs. 20, 21)
Ethmorhabdus sp. 1
Remarks. This small form of Ethmorhabdus has three cycles of small perforations. It differs from Ethmorhabdus gallicus (two cycles of perforations) by being smaller and by having fewer perforations arranged in three cycles.
Genus FLABELLITES Thierstein, 1973
Flabellites oblongus (Bukry, 1969) Crux, 1982
Watznaueria oblonga Bukry, 1969, p. 33, pl. 11, figs. 11-12.
Flabellites biforaminis Thierstein, 1973, p. 41, pl. 5, figs. 1-12.
Flabellites oblonga (Bukry, 1969) Crux, 1982, p. 110, pl. 5.1, fig. 11; pl. 5.8. fig. 1.
Remarks. Early morphotypes of Flabellites oblongus were observed in the upper Barremian to basal Aptian of ODP Hole 897C. These specimens differ from typical Flabellites oblongus by their reduced flanges and higher bar angles.
Genus GRANTARHABDUS Black, 1971
Grantarhabdus bukryi Black, 1972
(Pl. 8, Figs. 22, 23)
Genus HEXAPODORHABDUS Noël, 1965
Hexapodorhabdus cuvillieri Noël, 1965
(Pl. 11, Figs. 1, 2, 4-7)
Genus MARKALIUS Bramlette and Martini, 1964
Markalius ellipticus Grün in Grün and
Allemann, 1975
(Pl. 10, Figs. 1, 2, 4-7)
Genus MICROSTAURUS Black, 1971
Microstaurus chiastus (Worsley, 1971) Grün in Grün and
Allemann, 1975
(Pl. 8, Figs. 20, 21)
Genus MIRAVETESINA Grün in Grün and Allemann, 1975
Miravetesina favula Grün in Grün and
Allemann, 1975
(Pl. 8, Figs. 26, 27)
Genus NODOSELLA Prins, 1969 ex Rood, Hay, and Barnard, 1973
Nodosella cf. N. silvaradion (Filewicz et al. in Wise and Wind, 1977) Perch-Nielsen, 1984
Remarks. This form has a broad rim and a wide central area. It differs from typical Nodosella silvaradion by the absence of a central spine. The high number of bars forming a central platform and its thicker rim distinguish it from Stradnerlithus species. This form is very rare in lower Tithonian sediments from Hole 901 A.
Genus OCTOPODORHABDUS Noël, 1965
Octopodorhabdus praevisus Noël, 1965
(Pl. 11, Figs. 8, 9)
Octopodorhabdus praevisus Noël, 1965, p. 107, text fig. 31.
Remarks. The type specimen illustration of Octopodorhabdus praevisus is a hand drawing of a specimen with eight central perforations; two of these perforations fall in the longitudinal axis of the ellipse. However, the diagnosis of Octopodorhabdus praevisus (Noël, 1965, p. 107) indicates that the bars are aligned with the ellipse axes. Specimens attributed to Octopodorhabdus praevisus in the current study conform to the hand illustration of the holotype. Six large perforations are always clearly identifiable, whereas the two small aligned perforations tend to fall in the minor ellipse axis.
Genus PALAEOPONTOSPHAERA Noël, 1965 emended de Kaenel and Bergen, 1993
Remarks. Both de Kaenel and Bergen (1993) and Varol and Girgis (1994) emended Palaeopontosphaera to include those Biscutaceae with an inner distal wall. This inner wall displays a bright first-order white birefringence. Two Cretaceous species, which conform to the emended concept of this genus, are transferred to Palaeopontosphaera herein.
Palaeopontosphaera dorsetensis Varol and
Girgis, 1994
(Pl. 3, Figs. 15, 16)
Palaeopontosphaera dorsetensis Varol and Girgis, 1994, p. 243, fig. 8 (A, B), fig. 11 (7, 8).
Palaeopontosphaera dubia Noël, 1965
(Pl. 3, Figs. 12-14)
Palaeopontosphaera dubia Noël, 1965 (partim), p. 76-78, pl. 7, figs. 1, 2 (?), 5, 7-10 (non pl. 7, figs. 3, 4, 6, 11-13).
Palaeopontosphaera dubia Noël, 1965; de Kaenel and Bergen, p. 881-882, pl. l,fig. 15).
Palaeopontosphaera elliptica (Górka, 1957) comb. nov.
Tremalithus ellipticus Górka, 1957, p. 245, pl. 1, fig. 11.
Biscutum ellipticum (Górka, 1957) Grün and Allemann, 1975, p. 154-156, pl. 1, figs. 5-7, text fig. 3.
Remarks. Very small to small forms with a reduced central area and no central spine are identified as Palaeopontosphaera elliptica. In cross-polarized light, the tiny central plate exhibits a somewhat bright sigmoidal extinction line separating two darker points. This typical extinction pattern (due to the arrangement of the central granules) and absence of a spine differentiate Palaeopontosphaera elliptica from Palaeopontosphaera dubia.
Palaeopontosphaera erismata Wind and Wise in Wise and Wind, 1977
(Pl. 3, Figs. 17-19)
Palaeopontosphaera salebrosa (Black, 1971) comb. nov.
Cruciplacolithus salebrosus Black, 1971, p. 397, pl. 30, fig. 4.
Crucibiscutum salebrosum (Black, 1971) Jakubowski, 1986, p. 38, pl. 1, figs. 16-17.
Remarks. This species is transferred to the genus Palaeopontosphaera based on the presence of an inner distal wall. It differs from Palaeopontosphaera erismata by its larger size and distinct axial cross structure. Palaeopontosphaera salebrosa was observed in Holes 897C, 897C, and 899B.
Palaeopontosphaera sp. 1
Remarks. In cross-polarized light, this small form of Palaeopontosphaera has a bicyclic rim extinction pattern and a faint central plate with two small perforations aligned with the longitudinal axis. The FO of Palaeopontosphaera sp. 1 was observed in the upper Aptian in Hole 897C.
Palaeopontosphaera sp. 2
Remarks. This small circular to subcircular form of Palaeopontosphaera has a central cross supporting a solid distal projection, which nearly filled the central area. In cross-polarized light, Palaeopontosphaera sp. 2 exhibits a bicyclic rim. The thin inner rim cycle displays a first-order white birefringence, and the broad outer rim cycle is faintly birefringent. The central cross is also brightly birefringent.
Palaeopontosphaera sp. 2 differs from Palaeopontosphaera dorsetensis by the presence of a central structure.
Genus PERCIVALIA Bukry, 1969
Percivalia arata sp.
nov.
(Pl. 8, Figs. 3, 12, 14, 15)
Diagnosis. A medium-sized species of Percivalia with a narrow rim and a central area constructed by numerous, bladed elements arranged in longitudinal rows. A tiny central spine is present.
Description. The narrowly elliptical murolith has a narrow rim. The distal shield is low and very narrow; it is constructed of numerous, imbricated elements. The central area is filled with several longitudinal rows of upright, plate-shaped elements. A cycle of elements visible at the outer margin of the central area may represent the proximal shield. A tiny spine projects distally from the center.
The rim exhibits a faint birefringence and the central area is dark when specimens are oriented 45° to the polarizing direction. When parallel to the nicols, the central area becomes faint to weakly birefringent. Distinct longitudinal furrows separate the rim and central area.
Size. 6.0 to 7.0 μm (holotype: 6.7 (am).
Differentiation. Percivalia arata is the only known Jurassic species of Percivalia. It distinguished from Rhagodiscus nebulosus Bralower, 1989 (in Bralower et al., 1989) and Percivalia fenestrata (Worsley, 1971) Wise, 1983 by the orientation and optical properties of its central area elements (i.e., the longitudinal furrows).
Derivation of name. From Latin, arare: to plow.
Holotype. Plate 8, Figure 3.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; early Tithonian
Occurrence. Rare in Tithonian sediments from ODP Hole 901 A.
Genus PICKELHAUBE Applegate, Covington, and Wise in Covington and Wise, 1987
Pickelhaube furtiva (Roth, 1983) Applegate, Covington, and Wise in Covington and Wise, 1987
(Pl. 8, Figs. 18, 19)
Genus POLYPODORHABDUS Noël, 1965
Polypodorhabdus escaigii Noël, 1965
(Pl. 8, Figs. 10, 11)
Genus PERISSOCYCLUS Black, 1971
Perissocyclus noeliae Back, 1971
(Pl. 11, Fig. 19)
Genus RETECAPSA Black, 1971 emended Grün, 1975
Retecapsa neocomiana Black 1971
(Pl. 8, Figs. 16, 17)
Retecapsa neocomiana Black, 1971, p. 410, pl. 33, fig. 3.
Polypodorhabdus beckii Medd, 1979, p. 66, pl. 6, fig. 6.
Remarks. Retecapsa neocomiana is reserved for specimens having lateral bars that form eight angular openings of equal size. Polypodorhabdus beckii was described for forms with one or two lateral bars in each central quadrant, but its holotype looks nearly identical to that of Retecapsa neocomiana. Cretarhabdus octofenestratus Bralower, 1989 has circular central openings. Retecapsa angustiforata has a much larger central area, circular central openings, and very birefringent axial and lateral bars.
Retecapsa schizobrachiata (Gartner, 1968) Grün, 1975
Vekshinella schizobrachiata Gartner, 1968, p. 31, pl. 13, figs. 10, 11; pl. 20, fig. 5.
Cretarhabdus schizobrachiatus (Gartner, 1968) Bukry, 1969, p. 36, pl. 15, figs. 4-6.
Retecapsa schizobrachiata (Gartner, 1968) Grün, in Grün and Allemann, 1975, (non text fig. 17b).
Cretarhabdus schizobrachiatus (Gartner, 1968) Bukry, 1969. Bralower, Monechi, and Thierstein, 1989, p. 212, pl. 3, fig. 16.
Remarks. The emended concept of Retecapsa by Grün (in Grün and Allemann, 1975) included forms with eight or more central openings. Retecapsa schizobrachiata is distinguished by an axial cross that trifurcates longitudinally near the inner rim margin. This creates eight central area perforations of unequal size. The length of specimens recovered from Hole 901A range between 5 and 8 μm. Retecapsa schizobrachiata is very rare in Tithonian sediments from Hole 901 A. Grün and Zweili (1980) reported this species from the lower Oxfordian; the holotype was recovered from the Upper Cretaceous.
Genus RHAGODISCUS Reinhardt, 1967
Rhagodiscus achlyostaurion (Hill, 1976) Doeven, 1983
Parhabdolithus achlyostaurion Hill, 1976. p. 145. pl. 9, figs. 24-29.
Rhagodiscus achlyostaurion (Hill, 1976) Doeven, 1983, p. 50.
Remarks. Early morphotypes of Rhagodiscus achlyostaurion are distinguished by their smaller size (less than 5 μm) and relatively small central area. In cross-polarized light, the species is distinguished by (1) a circular spine base that appears as a bright circle with a dark center and (2) a narrow, birefringent inner rim cycle. Bergen (1994) recovered early morphotypes of R. achlyostaurion from the upper Barremian of DSDP Hole 534A and the Barremian stratotype. This event is used herein to subdivide the Micrantholithus hoschulzii Zone (CC6).
Rhagodiscus angustus (Stradner, 1963) Reinhardt, 1971
Remarks. Early morphotypes of Rhagodiscus angustus are very small and possess narrowly elliptical to subrectangular outlines. More typical forms have parallel longitudinal peripheries, which should be slightly concave. The FO of R. angustus (early morphotype) is slightly above that of Hayesites irregularis in Holes 897C and 899B, whereas it is 2.2 m below the FO of H. irregularis in Hole 897D. This could result from poor core recovery within the Cretaceous or the sporadic occurrence of H. irregularis near the bottom of its stratigraphic range.
Rhagodiscus pseudoangustus Crux, 1987
Rhagodiscus pseudoangustus Crux, 1987, p. 31, pl. 1, figs. 4, 5, 16, 17.
Zeugrhabdotus? pseudoangustus Bralower, Applegate, Covington, and Wise in Covington and Wise, 1987, p. 633, pl. 8, figs. 2-4.
Remarks. Rhagodiscus pseudoangustus is identified by its subrectangular outline and large, hollow spine. Rhagodiscus angustus has a subrectangular outline with parallel longitudinal peripheries that are slightly concave. It differs from R. pseudoangustus by its thick granular plate and the absence of a large, hollow spine. However, the electron micrograph of a specimen in proximal view illustrated by Crux (1987; pl. 1, fig. 5) shows the presence of a central granular plate. A central plate is not visible in the holotype (distal view) designated by Crux (1987; pl. 1, fig. 4), nor are any visible in the original specimens illustrated and described under the same species name by Bralower et al. (in Covington and Wise, 1987). Bralower et al. (in Covington and Wise, 1987) also commented on the absence of a central granular plate in their description of Zeugrhabdotus? pseudoangustus. Both publications became available in 1987. Rhagodiscus pseudoangustus Crux, 1987 was described in April 1987 and has priority over Zeugrhabdotus? pseudoangustus Bralower et al. (in Covington and Wise; May 1987). The designated holotype of Rhagodiscus pseudoangustus Crux, 1987 is better preserved and the presence of a thin, granular plate is assumed to be a preservational artifact.
Genus ROTELAPILLUS Noël, 1973
Rotelapillus pleoseptatus sp.
nov.
(Pl. 9, Figs. 14, 19-25)
Diagnosis. A small, elliptical species of Rotelapillus with a high distal shield and distally extended radial bars.
Description. A small elliptical murolith with a high distal shield constructed of vertical elements. The distal rim surface is irregular; its individual elements have pointed extremities of unequal length. The central area is constructed of thick, vertical elements that extend radially from the wall toward the center, but may not be joined at the center (preservational artifact?). In cross-polarized light, the rim is faintly birefringent and the radial central elements exhibit a first-order white birefringence.
Size. 4 to 5 μm (holotype: 4.6 μm).
Differentiation. Rotelapillus pleoseptatus differs from Rotelapillus radians by its elevated rim and by the higher number of radial bars. It differs from Rotelapillus laffittei by its high rim and elliptical shape. Rotelapillus pleoseptatus is differentiated from Rotelapillus caravacaensis by its higher number of radial bars.
Derivation of name. From Latin, pleto: column, and septum: partition.
Holotype. Plate 9, Figures 14, 22-25; specimen transferred from the LM to the SEM.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian
Occurrence. Rare to few in Tithonian sediments from ODP Hole 901 A.
Rotelapillus radians Noël, 1973 (Pl. 9, Figs. 3, 15-18)
Remarks. Rotelapillus radians is an elliptical to subelliptical species with eight radial bars and a low distal shield without any lateral projections. In cross-polarized light, the rim of Rotelapillus radians displays a bright, unicyclic birefringence. Rotelapillus radians differs from Rotelapillus caravacaensis (Grün in Grün and Allemann, 1975) by its narrower and lower distal shield. However, specimens of R. radians recovered from Hole 901A have slightly broader distal shields than illustrated by Noël (1973) and are difficult to differentiate from R. caravacaensis.
Genus STEPHANOLITHION Deflandre, 1939
Stephanolithion bigotii Deflandre, 1939 bigotii (Medd, 1979)
(Pl. 9, Figs. 1, 4, 5)
Genus STRADNERUTHUS Black, 1971
Stradnerlithus asymmetricus (Rood, Hay, and Barnard, 1971)
Noël, 1973
(Pl. 9, Figs. 2, 6, 7)
Stradnerlithus sexiramatus (Pienaar, 1969) Perch-Nielsen, 1984
(Pl. 9, Figs. 8, 9)
Genus TETRAPODORHABDUS Black, 1971
Tetrapodorhabdus coptensis Black, 1971
(Pl. 11, Figs. 12, 13)
Genus TRANOLITHUS Stover, 1966
Tranolithus incus sp.
nov.
(Pl. 7, Figs. 1,4,7-8)
Diagnosis. A small- to medium-sized, elliptical species of Tranolithus with four small blocky elements distributed on either side of the longitudinal poles and surrounding a broad, proximal bar (which almost fills the central area). Two small triangular openings are situated on each side of this plate bar.
Description. Elliptical murolith with a broad distal shield constructed of imbricated elements. Four blocky, rectangular elements are attached to the inner rim margin and are situated in pairs on either side of longitudinal poles. A thin, rectangular bar spans the central area and is attached to the proximal surface. In cross-polarized light, the rim extinction pattern is unicyclic and faintly birefringent. The four blocky central area elements are slightly more birefringent. The central plate is dark and is visible only in phase contrast illumination.
Size. 4.5 to 6.0 μm (holotype: 5.0 μm)
Differentiation. Tranolithus incus differs from other Tranolithus by its anvil-shaped central opening, proximal bar, and distribution of its four, blocky central elements. Rhagodiscus pseudoangustus has a subrectangular outline.
Derivation of name. From Latin, incus: anvil.
Holotype. Plate 7, Figures 1, 4.
Type locality. ODP Site 901, Iberia Abyssal Plain.
Type level. ODP Sample 149-901A-5R-1, 31 cm; Tithonian
Occurrence. Rare in Tithonian sediments from ODP Hole 901 A.
Genus TRISCUTUM Dockerill, 1987
Triscutum cf. T. expansum (Medd, 1979)
Dockerill, 1987
(Pl. 8, Figs. 6-9)
Remarks. This medium-sized form of Triscutum has a central grill composed of thin diagonal bars separated into four quadrants. It differs from typical specimens of Triscutum expansum by its narrow rim and inner wall. In cross-polarized light, the rim extinction pattern exhibits a first-order white bi-refringence. The four quadrants of the central grill exhibit a faint to white birefringence upon rotation, as opposing quadrants display the same birefringence. Triscutum cf. T. expansum is very rare to rare in Tithonian sediments from Hole 901 A, but its distinct optical properties enhance its potential biostratigraphic utility.
Genus THURMANNOLITHION Grün and Zweili, 1980
Thurmannolithion clatratum Grün and
Zweili, 1980
(Pl. 8, Figs. 1, 2, 4, 5)
Genus TRUNCATOSCAPHUS Rood, Hay, and Barnard, 1971
Truncatoscaphus senarius (Wind and Wise in Wise and Wind, 1977) Perch-Nielsen, 1984
(Pl. 9, Figs. 10, 11)
Genus VAGALAPILLA Bukry, 1969
Vagalapilla parallela (Wind and Cepek, 1979) comb. nov.
Rhadolekiskus parallelus Wind and Cepek, 1979, p. 232, pl. 3, figs. 3-6.
"Rhadolekiskus parallelus "Wind and Cepek, 1979; Covington and Wise, 1987, p. 632, pl. 23, figs. 3-5.
Vekshinella parallela (Wind and Cepek, 1979) Applegate and Bergen, 1988, p. 316, pl. 15, figs. 1-9.
Remarks. Applegate and Bergen (1988) demonstrated that the long distal projection of this species is supported by a thin axial cross and placed it within Vekshinella Loeblich and Tappan, 1963. Vagalapilla Bukry, 1969 is used herein for this group of muroliths because Vekshinella is based on a questionable type species and holotype.
Applegate and Bergen (1988) reported Vagalapilla parallela in the lower Valanginian of Leg 103 material. Bergen (1994) indicated an early Valanginian appearance for the species in southeastern France and DSDP Hole 534A. The occurrence of Vagalapilla parallela in Tithonian section of Hole 901A extends it range into the Jurassic.
Vagalapilla quadriarculla (Noël, 1965) Roth, 1983
(Pl. 10, Figs. 17, 18)
Vagalapilla stradneri (Rood, Hay, and Barnard, 1971) Thierstein 1973
(Pl. 10, Fig. 20)
Vagalapilla sp. 1
(Pl. 10, Figs. 15, 16)
Remarks. This small form (4.0 to 4.5 μm) of Vagalapilla has a inner rim cycle and a thin axial cross that exhibit a first-order white birefringence. The outer-rim cycle has a faint birefringence. In Vagalapilla stradneri (Pl. 10, Fig. 20), both the rim cycles and the axial cross have a similar faint birefringence. Vagalapilla quadriarculla differs from Vagalapilla sp. 1 by its arched axial cross bars and by its large circular central perforation.
Vagalapilla sp. 1 is rare to few in Tithonian sediments from Hole 901 A.
Vagalapilla sp. 2
Remarks. This small form of Vagalapilla has a bright bicyclic rim extinction pattern with a relatively large inner cycle exhibiting a first-order white birefringence and divided in four by radial extinction lines. The bright axial cross almost fills the central area and exhibits the same birefringence as the inner rim. Vagalapilla sp. 2 has its FO in the lower Aptian at Holes 897C, 897D, and 899B.
Vagalapilla sp. 3
(Pl. 10, Figs. 19, 21)
Remarks. In cross-polarized light, Vagalapilla sp. 3 has a bright bicyclic rim extinction and a groad acial cross, which displays a first-order white birefringence. Vagalapilla sp. 3 differs from other Jurassic Vagalapilla by its bright cross that nearly filled the central area.
Genus WATZNAUERIA Reinhardt, 1964
Watznaueria tubulata (Grün and
Zweili, 1980) comb. nov.
(Pl. 3, Figs. 9-11)
Ellipsagelosphaera? tubulata Grün and Zweili, 1980, p. 258, pl. 3, figs. 5-7, text fig. 16.
Remarks. This elliptical to subelliptical form is transferred to Watznaueria owing to its open and empty central area. Watznaueria tubulata differs from other Watznaueria with open central areas in the construction of its distal shield. As illustrated by Grün and Zweili (1980; text fig. 16) and on Plate 3, Figure 9, the elements of the outer distal cycle are vertically elongated and the shield has a tube shape rather than the flat distal shield observed in Watznaueria ovata.
Genus THORACOSPHAERA Kamptner, 1927
Thoracosphaera sp. 1
(Pl. 10, Figs. 3, 8-12)
Remarks. This spherical form referred to Thoracosphaera is similar in size to calcareous dinophytes from Upper Triassic sediments. Thoracosphaera sp. 1 has a small, hollow center and a thick test composed of large rhombic elements. In cross-polarized light, the elements of the test appear radially arranged and pseudo-extinction crosses are observed.