Fig. 16. An enlargement of the cardinal region; showing the deltidial plates 
and the encroachment of the foramen on the substance of the 
valve. The sharp definition of the cardinal area in this figure is 
erroneous. 
Fig. 19. A portion of the specimen represented in figure 15 enlarged to show 
more distinctly the structure of this process. ~ 6. 
Hudson River group. Versailles, Indiana. 
ZYGOSPIRA PUTILLA, Hall. 
Figs. 17, 18. Dorsal and ventral views of a typicalexample. * 2. 
Hudson River group. Pike county, Missouri. 
ZYGOSPIRA RECURVIROSTRA, Hall. 
Fig. 20. Profile view of an average example. ~ 3. 
Trenton limestone. Savannah, Illinois. 
Fig. 21. Dorsal view of a more finely plicated shell. X 2. 
Trenton horizon. Frankfort, Kentucky. 
ZyGosprgA CINCINNATIENSIS, Meek. 
Figs. 22, 23. Dorsal and ventral views of the exterior. 2. 
Hudson River group, Otincinnati, Ohio. 
ZYGOsPIRA KENTUCKIENSIs, James. 
Figs. 24, 25. Dorsal and profile views of a characteristic example, natural 
size. 
Hudson River group. Oldham county, Kentucky. 
CATAZYGA, Hatt. 
Page 813. 
Carazyea Hrant, Billings. 
Figs. 26, 27, 28. Dorsal, profile and cardinal views of the exterior. 
Hudson River group. Near Ottawa, Canada. 
Fig. 33. The interior of a portion of the pedicle-valve ; showing the deep mus- 
cular scar. 
Hudson River group. Waynesville, Indiana. 
Catazyca Heani, var. ANnTICOSsTIENS!Is, Billings. 
Figs. 29, 30, 31. Dorsal, ventral and profile views of an average example. 
Hudson River group. Collingwood, Ontario. 
Catazyca Heap, var. Borgatis, Billings, 
Fig. 32. Dorsal view ; showing the form of the shell. 
Anticosti group. Island of Anticostt. 
234 
