PLATE I— Continued. 



AviCULOPECTEX PRIXCEPS. 

 Page 1. 

 See Plates 5, 6, 21 and 81. 

 Fig. 10. A left valve. 



Upper Helderberg group. Falls of the Ohio. 

 Fig. 11. A larger left valve of this species. The Mnge-line should be represented as straight. 

 Upper Helderberg group. Bearyrass creek, Ky. 



PTERINOPECTEX D1GXATUS. 

 Pa^e 62. 

 Fig. 12. A left valve, enlarged to two diameters, showing the form and surface characters. 

 Fig. 14. A specimen retaining both valves, enlarged t.i two diameters, showing their comparative term and 

 surface ornamentation. The anterior ear of tie' right valve has much stronger rays than 

 represented. 

 Fig. 15. An imperfect left valve, natural size. 



Marcellus shale. Bloomfield. Ontario Co., N. 1". 



Pterinopectex L.ETUS. 



Page 63. 

 Fit;-. 13. The left valve of the specimen described, X 2. The umbo should be represented as tree from 

 radii, and concentrically wrinkled. 



Marcellus shale. Bloomfield. Ontario Co., X. Y. 



Pterixopecten EXFOLIATUS. 

 Page 61. 

 See Plate 83. 

 Fig. It;. 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 (PtERINOPECTEX '?) INVALIDl (8. 

 Page 31. 



See Plate 82. 

 Fig. IS. A left valve, X 2. Fig. 21. plate 82, gives a more entire outline of this species and of the natural 

 size. 



Marcellus shale, f/ierry Valley, JV. Y. 



