As mentioned previously, Quaternary placoliths in Sample 183-1139A-1CC as well as those in Samples 183-1139A-2R-3, 25-26 cm, and 2R-4, 25-26 cm, exhibited features that closely resemble E. huxleyi, although they lie stratigraphically well below the range of that taxon. Hence, the specimens in Sample 183-1139A-1-CC were examined with the SEM in order to resolve this apparent discrepancy.
The micrographs revealed small placoliths similar in construction to gephyrocapsids but etched so that their radial shield elements are well separated along their outer margins (Pl. P1; figs. 5, 6). As such, these elements superficially mimic the "I-bar" construction of E. huxleyi (cf., Malinverno et al. 2001, figs. 1 and 2, who also illustrate diagenetic modifications of this taxon). Etching, combined with the small size of our specimens, caused them to be confused with E. huxleyi during our initial light-microscope investigations. Identifications are particularly difficult if the centers of the specimens have also been enlarged by etching. This is not the case, however, in specimens where the central area has been thickened by secondary diagenetic overgrowth (e.g., Pl. P1; fig. 7).
The SEM micrographs further revealed larger placoliths in the assemblage attributable to Reticulofenestra and possibly Gephyrocapsa (Pl. P1; figs. 10, 11), with heavily etched centers and outer elements separated by etching. In the light microscope, these specimens might well mimic P. lacunosa, which displays a variable number of slits between its elements (e.g., Hine and Weaver, 1999; pl. 9.2, fig. 8).
Although the identifications of Gephyrocapsa in Plate P1 (figs. 5, 6) are somewhat tentative, other specimens in the assemblage can be more positively attributed to that genus. A wide range of preservational states is displayed in Plate P2. The example in Plate P2 (fig. 3) is unquestionably a gephyrocapsid, as the outer portions of its central area bar are clearly present. Its outer distal shield elements, however, are widely separated by etching, much like those in Plate P1 (figs. 5, 6), thereby demonstrating that etched gephyrocapsids can indeed mimic E. huxleyi.