PLATE 57. 
1. 456. 27. Atrypa neglecta. ( Pag. 274.) 
1 a, b. Yentral 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. 
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. 
3. 635. 49. Atrypa bidentata. ( Pag. 276.) 
3 a, b. Yentral 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. 
4. 636. 50. Atrypa cuneata. ( Pag. 276.) 
4 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 e. 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 striae. 
5. 637. 51. Atrypa-? (Pag. 277.) 
5 a. Yentral view. 5 b. Dorsal view, showing the simple direct plications. 
6. 638. 52. Atrypa disparilis. (Pag. 277.) 
6 a, b. Young individuals with scarcely two defined plications on each side of the centre. 
6 c, d. Yentral and dorsal valves of a specimen, with three plications on each side of the central pair. 
6 e. Another specimen having four plications. 
6 f. 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 the same enlarged. 
6 l, m. The interior of a ventral valve, and the same enlarged. 
7. 642. 56. Atrypa aprinis. (Pag. 280.) 
7 a, b. Yentral 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 striae. 
