PLATE 57. 



Fig. 1. 456. 27. Atrypa neglecta. (Pag- 274.) 



1 a, b. Ventral and front views of a young specimen, where the valves are equal and without a sinus. 

 1 c. A somewhat larger specimen, where the sinus and elevation are slightly developed. 

 1 d-h. Figures of specimens presenting varieties of form and size, and number of plications in the sinus. 

 1 i- m. Profile views of specimens which are not compressed. 



1 n, o, p. Front views showing the elevation of the plications, and the depression of the same in the sinus. 



Fig. 2. 634. 48. Atrypa interplicata. (Pag. 275.) 



2 a. Dorsal valve of this species. 



2 b. Dorsal view, where the ventral valve near the beak is elevated above the beak of the dorsal valve. 



2 c, d. Profile views of the specimens 2 a, b. 



2 e, f. Front views of two specimens, one of which is compressed. 



2 g. An enlargement of several plications, showing the interplications and concentric striae. 



Fig. 3. 635. 49. Atrypa bidentata. ( Pag. 276.) 



3 a, 6. Ventral and dorsal views of the same specimen. 



3 c, d. Similar views of a larger individual. 3 e, f. Profile views of a young and old individual. 



3 g. Front view of a specimen, showing the sinus and slight elevation. 



3 h. Several plications enlarged to show the surface markings. 



Fig. 4. 636. 50. Atrypa cuneata. (Pag. 276.) 



i a, b. Ventral views of two specimens of this species. 



4 c, d. Dorsal views of a specimen of ordinary size, and of another of very large dimensions. 

 4 c. Dorsal view of a specimen having a greater proportional width than usual. 



4 /, g, h. Profile views of specimens of different size. 



4 i. Profile of fig. 4 e, showing the great depth of the ventral valve. 



4 k -p. Front views of young and old specimens. 



4 r. Several plications enlarged, showing the concentric filiform strias. 



Fig. 5. 637. 51. Atrypa ? (Pag. 277.) 



5 a. Ventral view. 5 6. Dorsal view, showing tlie simple direct plications. 



Fig. 6. 638. 52. Atrypa d:sparilts. (Pag. 277.) 



Q a, b. Young individuals with scarcely two defined plications on each side of the centre. 



6 c, d. Ventral and dorsal valves of a specimen, with three plications on each side of the central pair. 

 6 e. Another specimen having four plications. 



6 /. Profile view of a full grown individual. 6 g. Front view of a specimen. 



6 h. The beak and foramen of the dorsal valve. 



6 i, k. The interior of a dorsal valve, and tlie same enlarged. 



6 I, m. The interior of a ventral valve, and the same enlarged. 



Fig. 7. 642. 56. Atrypa aprinis. ( Pag. 2S0.) 



7 a, b. Ventral and dorsal views of the specimen. 7 c. Profile view of the same. 

 7 d. Front view of the same. 7 e. Enlargement of the beak of the dorsal valve. 

 7 /. View showing the elevation of the striae. 



7 g. Several plications enlarged, showing the concentric striaj. 



