PLATE 55. 



Fig. 1. 627. 41. Atrypa NiTiDA. (Pag. 268.) 



1 a, h, c. Ventral views of three individuals of small size. 1 d. Profile view of fig. 1 c. 



1 €. A gibbous specimen, where the outline is narrow in proportion to the length. 

 1 /. 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. 

 1 Z. A large individual of the same species. 

 1 m, n. Profile and cardinal views of other specimens. 



1 0. Ventral view of a large specimen, which is inequilateral from pressure. 



Fig. 2. 628. 42, Atkypa nitida, var. oblata. ( Pag. 269.) 



2 a. Ventral view of a specimen of this variety. 2 6. Dorsal view of a large specimen. 



2 c. Profile view of the same. 



Fig. 3, 629. 43. Atkypa {Species undetermined). ( Pag. 269.) 



8 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. 



Fig. 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. 



Fig. 5. 460. 31. Atrypa reticularis. ' (Pag. 270.) 



5 a. A young individual of this species. 6 6. Cardinal view, showing the compressed form. 

 5 c. A larger individual . 5 d, e. Cardinal and profile views of the same. 



5 /, s, 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 fe, I, in. Ventral, profile, and cardinal view of a globose specimen of medium size. 



6 n, 0. Dorsal and front vievv, 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 u. A cast of the dorsal valve. 



