PLATE I—Continued. 
Aviculopecten PRINCEPS. 
Page 1. 
See Plates 5, 6, 24 and 81. 
Fig. 10. A left valve. 
Upper Helderberg group. Falls of the Ohio. 
Fig. 11. A larger left valve of this species. The hinge-line should be represented as straight. 
Upper Helderberg group. Beargrass creek, Ky. 
PTERINOPECTEN D1GNATUS. 
• Page 6-2. 
Fig. 12. A left valve, enlarged to two diameters, showing the form and surface characters. 
Fig. 14. A specimen retaining both valves, enlarged to two diameters, showing their comparative form and 
surface ornamentation. The anterior ear of the right valve has much stronger rays than 
represented. 
Fig. 15. An imperfect left valve, natural size. 
Marcellus shale. Bloomfield, Oniano Co., N. Y. 
Pterinopecten l^tus. 
, Page 63. 
Fig. 13. The left valve of the specimen described, X 2. The umbo should be represented as free from 
radii, and concentrically wrinkled. 
Marcellus shale. Bloomfield, Ontario Co., N. Y. 
Pterinopecten exeoliatus. 
Page 61. 
See Plate 83. 
Fig. 16. A medium sized left valve of this species. 
Limestone of the Marcellus shale. Avon, N. Y. 
Fig. 17. A large left valve, with the test more exfoliated than the preceding. 
Limestone of the Marcellus shale. Vienna, Ontario Co., N. Y. 
Aviculopecten (Pterinopecten ?) invalldus. 
Page 31. 
See Plate 82. 
Fig. 18. A left valve, X 2. Fig. 21, plate 82, gives a more entire outline of this species and of the natural 
size. 
Marcellus shale. Cherry Valley, N. Y. 
