PLATE 55. 



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



1 o, b, c. Ventral views of three individuals of small size. 1 d. Prolilc view uf fig. 1 c. 



1 e. A gibbous specimen, where the outline is narrow in proportion to tlie lengUi. 

 1 /. Profile view of the same sj>eciinen. 1 g. Front view of the .same. 



1 A, t, fc. Ventral, profile and front vicw.s of a specimen, where the valves are very much thickened to- 

 wards the bases. 

 1 /. A large imlividual 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. Atrtpa nitida, I'ar. oblata. ( Pag. 269.) 



2 a. Ventral view of a S[)ecimen of this variety. 2 b. Dorsal view of a large specimen. 



2 c. Profile view of the same. 



Fig. 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 dor-sal 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 e. Front view of the same. 



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



5 o. 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/, g, h. Ventral, prolile and front view of a specimen, .showing, in the last figure, the sliglil sinus in the 

 dorsal valve, and the elevation of the margin of the ventral valve. 



6 i. Profile view of a flattened specimen. 



6 k, /, m. Ventral, profile, and cardinal view of a globose specimen of medium size. 



6 n, Dorsal and front view, showthg the sinus more conspicuously than the preceding figure. 



6 p. A large individual ; view of the ventral valve. 



6 r. Profile view of the .same .specimen, which is compressed. 



6 ». The interior of the dorsal valve, showing the form of the mu.sciilar impression. 



6 t. Several of the plicatio;]S enlarged, showing more distinctly the character of the surface. 



6 u. A cast of the dorsal valve. 



