PLATE 57. 



Firr. 1. 456. 27. Atrypa neghecta. ( Panf. 274.) 



1 o, ft. Ventral and front views of a young specimen, where llie valves arc equal and without a sinus. 

 1 c. A somewhat larger S]iecimen, where the sinus and elevation are slightly developed. 

 1 rf - A. 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 H, 0, p. Front views showing the elevation of the plications, and the depression of the same in the sinus. 



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



2 a. Dorsal valve of this species. 



2 b. Dorsal view, where tlic ventral valve near tlio 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. 



An enlargement of several plie.itions, showing the intcrplications and concentric strix. 



o , 



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



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



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



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



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



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



■Jo,*. 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 /, s, h. Profile views of specimens of difierent 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 stria?. 



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



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



Fig. 6. 638. 52. Atrypa dispahilis. (Pag. 277.) 



6 a, ft. Young individuals with scarcely two defined i)licatiuns on each side of the centre. 



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



e. Another specimen having four plications. 



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



6 A. The beak and foramen of the dor.sal valve. 



6 t, k. The interior of a dorsal valve, and (he same enlarged. 



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



Fig. 7. 642. 56. Atrypa aprinis. ( Pag. 280.) 



7 a, ft. Ventral and dorsal views of the specimen. 7 r. 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 stria;. 



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



