PLATE 52. 
Figs. 1-12. Atrypa reticularis. . ... 
1-3. Dorsal, profile and cardinal views of an extremely gibbous form of this species, from the 
Falls of the 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 A. desquamata . of Sowerby, but the shells are more gibbous and the beaks less 
elevated. The foramen and deltidial area are not preserved in our species except in the 
young individuals. It is probable that they will eventually prove to be specifically dis¬ 
tinct from the smaller forms referred to A. reticularis. 
11. The interior of the ventral valve, showing muscular impressions and teeth. 
12. A cast of the ventral valve of a smaller specimen, showing the muscular and vascular 
markings. 
Figs. 13 - 19. CCELOSPIRA CAMILLA (CONCAVA of text).. 
13. 14. Dorsal and ventral views of a specimen having the ordinary size and characters of those 
from the Lower Helderberg 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 muscular^impressions and teeth; enlarged to four 
diameters. 
