Explanation of Plate 1 



Figs. 1-3 Acratia obtusa Cooper, n. sp. Dorsum, left valve, and venter of holotype, x30. 



Paint Creek formation, loc. 2 p. 24 



4-8 Triceratina inconsueta (Croneis and Gutke). 4 and 6, anterior and posterior ends; 



5, 7, and 8, left valve, venter, and dorsum, x40. Renault formation, loc. 9 . . p. 24 



9-10 Bairdia golcondensis Croneis and Gale. Dorsum and right valve, x40. Golconda 

 formation, loc. 17 



11-12 Bairdia brevis Jones and Kirkby. Dorsum and right valve, corroded along postero- 



dorsal slope, x20. Menard formation, loc. 15 p. 25 



13-16 Monoceratina furcula Croneis and Gale. 13, posterior end; 14-16, dorsum, right 

 valve, and venter, x40. Menard formation, loc. 28 



17-20 Bairdia granireticulata Harlton. Dorsum and right valve of two specimens from the 

 Paint Creek (17, 18) and Golconda formations (19, 20) ; x20. Localities 18 

 and 17 p. 26 



21-22 Bairdia aequa Cooper, n, sp. Dorsum and right valve of holotype, x30. Renault 



formation, loc. 13 p. 24 



23-26 Monoceratina celsalobata Cooper, n. sp. 23, posterior end ; 24-26, dorsum, right valve 



and venter of holotype, x40. Golconda formation, loc. 17 p. 23 



27-28 Bairdia cestriensis Ulrich. Dorsum and right valve, x20. Golconda formation, 



loc. 19 p. 25 



29-32 Monoceratina opima Cooper, n. sp. 29, posterior end; 30-32, dorsum, right valve 



and venter of holotype, x40. Renault formation, loc. 9 p. 23 



33-34 Bairdia attenuata Girty. Dorsum and right valve, x20. Glen Dean formation, loc. 1 p. 25 



35-37 Acratia tumida Cooper, n. sp. Dorsum, right valve, and venter of holotype, x30. 



Kinkaid formation, loc. 3 p. 24 



38-39 Bairdia galei Croneis and Thurman. Dorsum and right valve, x30. Kinkaid forma- 

 tion, loc. 28 



40-42 Acratia ?nucronata Cooper, n. sp. Dorsum, left valve and venter of holotype, x30. 



Glen Dean formation, loc. 1 ' p. 24 



43-44 Bairdia curvis Cooper, n. sp. Dorsum and right valve of holotype, x20. Paint Creek 



formation, loc. 32 p. 25 



45-46 Bairdia delicata Morey. Dorsum and right valve, x30. Menard formation, loc. 20 . p. 25 



47-48 Bairdia aculeata Cooper, n. sp. Dorsum and right valve of holotype, x30. Kinkaid 



formation, loc. 3 p. 24 



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