PLATE 28. 
Page 
Figs. 1-11. SPIRIFERA GREGARIA. 195 
1. Dorsal view of a young individual. 
2. A dorsal view of a specimen of the ordinary size and form. 
3-6. Ventral, dorsal, profile and front views, of a large and gibbous form. 
7, 8. Interiors of ventral valves. These specimens are from the Falls of the Ohio. - 
9, 10. Dorsal and cardinal views, of a cast of this species in chert, from Indiana. This speci¬ 
men shows a distinct depression in the mesial fold which is not a usual feature. 
11. The interior of a ventral valve and part of a dorsal, showing the crura and the last turns 
of the spire. From the Falls of the Ohio. 
Figs. 12-16. Spirifera Formosa. 220 
12 -16 Dorsal, cardinal, profile, front and ventral views of the typical specimen of the species. 
Figs. 17 -23. Spirifera grieri. 194 
17 - 20. Four views of a specimen of small or medium size. 
21. A dorsal view of a large specimen, showing several plications on the mesial fold. 
22. A ventral valve, where the hinge is much extended, and the plications are less defined in the 
mesial depression. 
23. A front view of the specimen fig. 21. 
In the collections of the Canadian Geological Survey, there is a specimen of this species 
of much larger size than those observed or figured among the New York collections. 
Figs. 24-33. Spirifera duodenaria. .... 189 
24. 26, 29, 30, 31. Dorsal, ventral, front, cardinal and profile views of a well formed and char¬ 
acteristic specimen of medium size. 
25. 28, 32. Dorsal, ventral and profile views of a more gibbous form. 
27. Ventral view of a large individual. 
33. The interior of a small ventral valve. 
