PLATE 53. 
Figs. 1, 2. Atrypa pseudomarginalis.. 3 
I, 2. Dorsal and ventral views of an individual of the species. 
Figs. 8-19. Atrypa reticularis..... 
3. Dorsal view of a young individual which preserves the deltidial plates. 
4. Enlargement of the beak of specimen, fig. 3, showing the deltidial plates and perforation 
of the beak. 
5-7. Yentral, dorsal and profile views of a specimen of medium size, of the ordinary form of 
those from the shales of the Hamilton group of New York. 
8. Ventral view of a larger individual, showing the extension of the lamellae on the sides of 
the shell. 
9. The interior of the dorsal valve, showing muscular impressions, hinge-plate, and crenulated 
socket plates. 
10. An enlargement of the cardinal portions of specimen fig. 9, more clearly showing the 
characters of the hinge and points for the attachment of the crura. 
II. The interior of a ventral valve, showing muscular impressions, teeth, etc 
The specimens, figs. 3-11, are all from the shales of the Hamilton group, of New York. 
12, 13. Dorsal and ventral views of a specimen, from Lime Creek, Iowa, supposed to be of the 
age of the Chemung group. 
14, 15. Dorsal and profile views of a large form, common to the Hamilton group, at Independ¬ 
ence, Iowa. 
16. View of a large individual from Waverly, Iowa. The dorsal valve has been broken away, 
revealing parts of the spiral band and the loop connecting the cones. 
17. Dorsal view of a well formed individual, from the Chemung group, of New York. 
18. An impression of the ventral valve of a more coarsely ribbed specimen, from the Chemung 
group, of New York. 
19. A cast of the ventral valve, of a very finely ribbed specimen, from the Chemung group. The 
form of the valve and the great extension of the cardinal border, presents considerable 
resemblance to those from Independence, Iowa; figs. 14, 15. 
