PLATE 52. 



Page 



Figs. 1 -12. Atiiypa reticularis, 316 



1-3. Dorsal, profile and cardinal views of an extremely gibbous form of this species, from tlio 



Falls of llie Ohio. 

 4 - 6. A very gibbous form with the ventral valve extremely elevated in front, and the surface 



with somewhat strong lamellose lines. Specimens from the Bake-oven, Illinois. 

 7-10. Dorsal, ventral and profile views of large gibbous forms, in the Corniferous limestone of 

 Albany and Schoharie counties. These specimens present many features in common 

 with the Jl- desquamata of Sowerby, but the shells are more gibbous and the beaks less 

 elevated. The foramen and deltidiul area are not preserved in our species except in tlie 

 young individuals. It is probable that they will eventually prove to bo specifically dis- 

 tinct from the smaller forms referred to ji. reticularis. 



11. The interior of the ventral valve, showing muscular imiiressions and teeth. 



12. A cast of the ventral valve of a smaller specimen, showing the muscular and vascular 



markings 



I'igS. 13-19. CtELOSPIRA CAMILLA (CONCAVA of text) 32f 



18. 14. Dorsal and ventral views of a specimen having the ordinary size and characters of those 



from the Lower Hclderbcrg group; enlarged to two diameters. 

 15-17. Dorsal, ventral and profile views of a larger and more coarsely plicated form; enlarged 



to two diameters. 



18. Interior of the dorsal valve, showing the cardinal process and dental sockets. 



19. Interior of the ventral valve, showing nin8cular_ impressions and teeth j enlarged to four 



diameters. 



