PLATE 53. 



Page 

 Figs. 1, 2. AtRYPA P8EUDOMAROINALI8 8:i7 



I, 2. Dorsal and ventral views of an individual of the spccius. 



Figs. 3-19. Atkypa reticularis '.lUi 



8. Dorsal view of a young individual wliich preserves the deltidial plates. 



i. Enlargement of the beak of specimen, fig. 3, showing the deltidial plates and perforation 



of the beak. 

 6-7. Ventral, 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 nf the lamella! on the sides of 



the shell. 



9. The interior of the dorsal valve, showing muscular impressions, hingt-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 gioup, of New York. 



12, 13. Dorsal and ventral views of a specimen, from Lime Creek, Iowa. su])posed 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 donsal v.alve 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, lowaj figs. 14, 15. 



