PLATE 55. 
1. 627. 41. Atrypa nitida. ( Pag. 268.) 
1 a, b, c. Ventral views of three individuals of small size. 1 d. Profile view of fig. 1 e. 
1 e. A gibbous specimen, where the outline is narrow in proportion to the length. 
1 f. Profile view of the same specimen. 1 g. Front view of the same. 
1 h, i, k. Ventral, profile and front views of a specimen, where the valves are very much thickened to- 
wards the bases. 
11. A large individual of the same species. 
1 m, n. Profile and cardinal views of other specimens. 
1 o. Ventral view of a large specimen, which is inequilateral from pressure. 
2. 628. 42. Atrypa nitida, var. oblata. ( Pag. 269.) 
2 a. Ventral view of a specimen of this variety. 2 b. Dorsal view of a large specimen. 
2 c. Profile view of the same. 
3. 629. 43. Atrypa-( Species undetermined). (Pag. 269.) 
3 a. Dorsal view of this species. 3 b. Front view of the same. 
3 c. Cast of the dorsal valve of a specimen having the general external features of this species. 
3 d. Cardinal view of the same. 3 e. Lateral view of the same. 
4. 630. 44. Atrypa crassirostra. ( Pag. 269;) 
4 a. Ventral view of a full grown specimen. 4 b. Profile view of the same. 
4 c. Front view of the same. 
5. 460. 31. Atrypa reticularis. (Pag. 270.) 
5 a. A young individual of this species. 5 b. Cardinal view, showing the compressed form. 
5 c. A larger individual. 5 d, e. Cardinal and profile views of the same. 
6 /, g, h. Ventral, profile and front view of a specimen, showing, in the last figure, the slight sinus in the 
dorsal valve, and the elevation of the margin of the ventral valve. 
6 i. Profile view of a flattened specimen. 
5 k, l, in. Ventral, profile, and cardinal view of a globose specimen of medium size. 
6 n, o. Dorsal and front view, showing the sinus more conspicuously than the preceding figure. 
5 p. A large individual: view of the ventral valve. 
5 r. Profile view of the same specimen, which is compressed. 
5 s. The interior of the dorsal valve, showing the form of the muscular impression. 
5 t. Several of the plications enlarged, showing more distinctly the character of the surface. 
6 «. A cast of the dorsal valve. 
