Plate P18. 1. Gerdiocysta conopeum Liengjarern et al. 1980. Dorsal view of dorsal surface (400x). 2–4. Glaphyrocysta semitecta (Bujak in Bujak et al. 1980) Lentin and Williams 1981. (2) ventral surface (400x); (3) same specimen as 2, optical section (400x); (4) same specimen as 2, dorsal surface (400x). 5. Gramocysta verricula (Piasecki 1980) Lund and Lund-Christensen in von Daniels et al. 1990. 425x. 6. Habibacysta tectata Head et al. 1989b. Dorsal surface (900x). 7, 8. Hemiplacophora semilunifera Cookson and Eisenack 1965a; (7) operculum (900x); (8) ventral view of dorsal surface plus operculum (500x). 9. Heteraulacacysta porosa Bujak in Bujak et al. 1980. 350x. 10, 11. Heterosphaeridium difficile (Manum and Cookson 1964) Ioannides 1986. Both 400x. 12–16. Homotryblium floripes (Deflandre and Cookson 1955) Stover 1975; (12) antapical view of antapical surface (350x); (13) same specimen as 12, antapical view of postcingular processes (350x); (14) same specimen as 12, antapical view of cingular processes (350x); (15) antapex (350x); (16) antapex (400x). 17, 18. Homotryblium tenuispinosum Davey and Williams 1966b; (17) lateral view (450x), courtesy of J.P. Bujak; (18) ventral surface showing sulcal tongue (450x). 19, 20. Hystrichokolpoma bulbosum (Ehrenberg 1838) Morgenroth 1968; (19) optical section (800x); (20) same specimen as 19, ventral surface in focus (800x), courtesy of S.P. Damassa.

Plate P18. 1. Gerdiocysta conopeum Liengjarern et al. 1980. Dorsal view of dorsal surface (400x). 2–4. Glaphyrocysta semitecta (Bujak in Bujak et al. 1980) Lentin and Williams 1981. (2) ventral surface (400x); (3) same specimen as 2, optical section (400x); (4) same specimen as 2, dorsal surface (400x). 5. Gramocysta verricula (Piasecki 1980) Lund and Lund-Christensen in von Daniels et al. 1990. 425x. 6. Habibacysta tectata Head et al. 1989b. Dorsal surface (900x). 7, 8. Hemiplacophora semilunifera Cookson and Eisenack 1965a; (7) operculum (900x); (8) ventral view of dorsal surface plus operculum (500x). 9. Heteraulacacysta porosa Bujak in Bujak et al. 1980. 350x. 10, 11. Heterosphaeridium difficile (Manum and Cookson 1964) Ioannides 1986. Both 400x. 12–16. Homotryblium floripes (Deflandre and Cookson 1955) Stover 1975; (12) antapical view of antapical surface (350x); (13) same specimen as 12, antapical view of postcingular processes (350x); (14) same specimen as 12, antapical view of cingular processes (350x); (15) antapex (350x); (16) antapex (400x). 17, 18. Homotryblium tenuispinosum Davey and Williams 1966b; (17) lateral view (450x), courtesy of J.P. Bujak; (18) ventral surface showing sulcal tongue (450x). 19, 20. Hystrichokolpoma bulbosum (Ehrenberg 1838) Morgenroth 1968; (19) optical section (800x); (20) same specimen as 19, ventral surface in focus (800x), courtesy of S.P. Damassa.