Explanation of Plate 5 



Figs. 1-6 Tetratylus ellipticus Cooper, n. sp. Dorsum, left valve and posterior end. Genotype 



(figs. 1-3), x40. Paint Creek formation, loc. 24 p. 35 



7 Tetratylus elongatus Cooper, n. sp. Left valve. Holotype, x40. Paint Creek forma- 

 tion, loc. 24 p. 35 



8-12 Tetratylus menardensis (Croneis and Bristol). 8, 9, left valve and posterior end, ' 



Menard formation, loc. 28 ; 10-12, dorsum, left valve and posterior end. Paint 

 Creek formation, loc. 24, x40 p. 35 



13-14 Beyrichia contracta Cooper, n. sp. Dorsum and right valve. Holotype, x40. Golconda 



formation, loc. 18 p. 35 



15-17 Beyrichia sagitta Cooper, n. sp. Dorsum, posterior end, and right valve. Holotype, 



x40. Paint Creek formation, loc. 2 p. 35 



18-19 Beyrichia placida Croneis and Gale. Dorsum and left valve, x40. Golconda forma- 

 tion, loc. 22 



20-21 Cavellina congruens Cooper, n. sp. Dorsum and left valve. Holotype, x30. Clore 



formation, loc. 4 p. 36 



22-23 Cavellina bransoni (Morey). Dorsum and right valve, x30. Kinkaid formation, 



loc. 3 p. 35 



24-25 Cavellina coryelli Croneis and Gale. Dorsum and left valve, x30. Clore formation, 

 loc. 4 



26-27 Ca'vellina hoeniri Coryell and Johnson. Dorsum and left valve, x40. Clore forma- 

 tion, loc. 4 



28-29 Cavellina dispar Cooper, n. sp. Dorsum and left valve. Holotype, x30. Menard 



formation, loc. 20 p. 36 



30-31 Cavellina parallela Croneis and Gale. Dorsum and left valve, x30. Paint Creek 

 formation, loc. 18 



32-33 Cavellina perplexa Croneis and Funkhouser. Dorsum and left valve, x30. Clore 

 formation, loc. 4 



34-36 Cavellina exila Cooper, n. sp. Dorsum, left valve, and posterior end. Holotype, 



x20. Renault formation, loc. 13 p. 36 



37-38 Cavellina librata Cooper, n. sp. Dorsum and left valve. Holotype, x30. Clore for- 

 mation, loc. 4 p. 36 



39-40 Cavellina parva Cooper, n. sp. Dorsum and left valve. Holotype, x30. Vienna 



formation, loc. 10 p. 37 



41-42 Cavellina longula Cooper, n. sp. Dorsum and left valve. Holotype, x30. Golconda 



formation, loc. 22 p. 36 



43-44 Cavellina geisi (Croneis and Gale). Dorsum and left valve, x30. Vienna forma- 

 tion, loc. 10 p. 36 



45-48 Cavellina ovatiformis (Ulrich). Dorsum and left valve. 45, 46, Kinkaid forma- 

 tion, loc. 5 ; 47, 48, Fayetteville shale, loc. 31, x30 p. 37 



49-50 Cavellina glandella (Whitfield). Dorsum and left valve, x30. Kinkaid formation, 



loc. 3 p. 36 



[76 



