PLATE XLV— Continued. 

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

 ginal inflexion on the cardinal slopes of the 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. Varioiis localities in the snft shaJes of Western New Turk. 

 Fig. 22. A dorsal view of an internal cast of conjoined valves, showing the impi'ession of the hinge-plate, 

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

 of the rostral cavil}' of the pedicle-valve. 



Hamilton group. Hardy euunty, Virgi7iia. 

 Fig. 23. A'ventral view of a jireparation of the brachidiuin ; showing the form of the spirals, the crui-a 



and their attachment to the primary lamellfe, and the accessory laraelliB. 

 Fig. 24. An internal cast of the pedicle-valve, slightly broken at the umbo ; showing the adductor and 



diductor impressions, and the vascular sinuses. 

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



Hamilton group. Varioits localities in tlie shales of Western New York. 



Athykis Angelica, Hall. 



Fig. 26. The exterior of a bi'achial valve. 



Fig. 27. The exterior of a pedicIe--\-alve. 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-jilate ; showing the straight anterior edge, the ci-ural plates, visceral 

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



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

 Chemung group. Belfast, N. Y. 



