PLATE 52. 



Fig. 1. 612. 25. Ortiiis pisuM. ( Pag. 250.) 



1 tf, b. Young specimens of this species. 



1 c. The ventral valve of a full grown individual, showing the beak of the dorsal valve. 



1 d. Profile view of the same, the shell slightly compressed. 1 e. View of the beaks of the same. 



Fig. 2. 613. 26. Orthis pyramidalis. (Pag. 251.) 



2 a, b, c, d. Dorsal, ventral, cardinal and profile views of a specimen of the ordinar)- size. 

 2 e, f, g, h. Similar views of a much larger shell. 



2 ('. An enlargement of the surface, showing the sharp plications crossed by concentric striae. 



Fig. 3. 440. 22. Orthis elegantula. ( Pag. 252.) 



3 a, b. The dorsal valves of young individuals. 



3 c. Tlie dorsal valve of a full grown individual, having the beak somewhat more extended than in other 



specimens. 

 3 d. Ventral view of the same specimen. 3 e. Profile view of the same specimen. 



3 /. Cardinal view of the same, showing the elevation of the dorsal valve. 

 8 g. Ventral view of a shorter specimen. 3 h. Cardinal view of the same. 



3 i. Cast of a dorsal valve of an elongated specimen. 3 k. Cardinal view of the same. 



3 I, m. The interior of the dorsal valves of a young and full grown individual. 

 3 n. The interior of a ventral valve, showing the muscular impresssion, lamella;, etc. 

 3 o. The same enlarged. Sp. The interior of a similar shell, showing a slight variation in character. 



3 r. Cardinal view of the same, showing the dental lamellaj, and the callosity at the apex of the foramen. 



3 s. An enlargement of the surface. 



Fig. 4. 614. 27. Orthis hybkida. ■ ( Pag. 253.) 



4 a, b, c. Figures of specimens showing three gradations of size. 

 4 d, e. Cardinal and profile views of fig. 4 c. 



4 /. A specimen having the valves more convex than usual. 



4 g. Profile view of the same specimen, showing the nearly equal convexity of the valves. 



4 A. A cardinal view of a specimen, showing the convexity of the dorsal valve. 



i i, k. The interior of the dorsal valve of this species, showing the muscular impression divided by a longi- 

 tudinal ridge. 



4 1, An enlargement of the muscular impression of the preceding specimen. 



4 m. The interior of the ventral valve, with a scarcely defined muscular impression. 



4 n. A cast of the ventral valve of this species, showing the bilobate character of the muscular impression, 

 the cavities of the teeth, etc. 



4 o. An enlargement of the surface, .showing the longitudinal diverging and fine concentric striae. 



Fig. 5. 615. 28. Orthis pdncto-striata. { Pag. 254.) 



5 a. View of the ventral valve of a small specimen, showing the beak of the dorsal valve, and a part of the 



area above it. 5 6. A profile view of the same specimen. 



5 c. A cardinal view of a larger specimen, showing the great convexity of the valves. 

 b d. A large dorsal valve which has been flattened by pressure. 5 e. The interior of the same. 



5 /. Several of the striae enlarged, showing the puncta between. 



Fig. 6. 616. 29. Orthis flabellulttm, Var.? ( Pag. 254») 



6 a, b, c. Dorsal, profile and ventral views of a compressed specimen. 



G d. Tlic interior of a ventral valve. 6 c. A cast of a ventral valve. 



6 /. Cardinal view of a specimen, which is partially a cast. 



6 g. Cardinal view of the specimen fig. 6 a. 



Fig. 7. 616. 29. Orthis FLABELLULUiu? Var.? ( Pag. 255.) 



7 a, b. Dorsal and ventral views of the specimen. 



7 c. Profile view of the same. 7 d. Cardinal view the same. 



Fig. 8. 617. 30. Outhis FA.«ciATA. (Tag. 255.) 



8 a. A cast of the ventral valve, showing an extended hinge-line. 8 6. A cast of the dorsal valve. 



