PLATE XLV— Continued. 

 Figs. 18, 19. Dorsal and cardinal views of a narrow and rather rotund individual. Fig. 19 shows the mar- 

 ginal inflexion on the cardinal slojies of (he pedicle-valve. 

 Fig. 20. Frontal view of a shell, showing about the minimum development of the median fold and sinus. 

 Fig. 21. Frontal view of a large example in which the development of median fold and sinus has virtually 

 attained its maximum. 



Hamilton group. Varimis localities in the soft shales of Western New York. 

 Rg. 22. A doiTsal view of an internal cast of conjoined valves, showing the impression of the hinge-plate, 

 the tilling of the visceral foramen, the muscular scars and vascular markings, and also the cast 

 of the rostral cavity of the pedicle-valve. 



Hamilton group. Hardy county, Virginia. 

 Rg. 23. A'ventral view of a preparation of the brachidium ; showing the form of the 8{>iral8, the crura 



and their attachment to the primary lamellae, and the accessory lamellse. 

 Fig. 34. An intei-nal cast of the pedicle-valve, slightly broken at the umbo ; showing the adductor and 



diductor impressions, and the vascular sinuses. 

 Rg. 25. The exterior of a transverse, coarsely lamellose individual. 



Hamilton group. Various localities in the s?iales of Western New York. 



Athykis Angelica, Hall. 



Fig. 26. The exterior of a brachial valve. 



Fig. 27. The exterior of a pedicle-valve. These figures show the fine, crowded concentric striae extending 

 from umbones to margins. 



Fig. 28. An internal cast of a pedicle-valve ; showing the filling of the deep pedicle-cavity, and the indis- 

 tinct scar of the diductors. 



Chemung group. Btlmont, N. Y. 



Fig. 29. Anterior view of the hinge-plate ; showing the straight anterior edge, the crural plates, visceral 

 foramen, and the elevation of the posterior portion of the surface. X 3. 



Fig. 30. A profile view of an old and giblx)us shell, with a few strong growth-lines. 

 Chemung group. Belfast, N. Y. 



