Figs. 18, 
Fig. 20. 
Fig. 21. 
Fig. 22. 
Fig. 23. 
Fig. 24. 
Fig. 25. 
Fig. 26. 
Fig. 27. 
Fig. 28. 
Fig. 29. 
Fig. 30. 
PLATE XLV—Continued. 
19. Dorsal and cardinal views of a narrow and rather rotund irfdividual. Fig. 19 shows the mar¬ 
ginal inflexion on the cardinal slopes of the piedicle-valve. 
Frontal view of a shell, showing about the minimum development of the median fold and sinus. 
Frontal view of a large example in which the development of median fold and sinus has virtually 
attained its'maximum. 
Hamilton group. Various'J.ocalities in the soft shales of Western New York. 
A dorsal 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. 
A'ventral view of a preparation of the brachidium; showing the form of the spirals, the crura 
and their attachment to the primary lamelljE, and the accessory lamellae. 
An internal cast of the pedicle-valve, slightly broken at the umbo; showing the adductor and 
diductor impressions, and the vascular sinuses. 
The exterior of a transverse, coarsely lamellose individual. 
Hamilton group. Various localities in the shales of Western Neio York. 
Athyris Angelica, Hall. 
The exterior of a brachial valve. 
The exterior of a pedicle-valve. These figures show the fine, crowded concentric striae extending 
from umbones to margins. 
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. Belmont, N. Y. 
Anterior view of the hinge-plate; showing the straight anterior edge, the crural jfiates, visceral 
foramen, and the elevation of the posterior portion of the surface. X 3. 
A profile view of an old and gibbous shell, with a few strong growth-lines. 
Chemung group. Belfast, N. Y. 
