PLATE VIII. 
Platyceras Argo. 
Page 19. 
Figs. 1-3. Three views of the originally described specimen; a partial internal cast, retaining the impres¬ 
sions of the concentric undulations of the surface. 
Fig. 4. View of the right side of a specimen, partially exfoliated. Along the middle can be traced the 
remains of a deep notch which existed in the lip, now forming an elevated ridge somewhat 
obscured by adhering rock. 
Fig. 5. View of the opposite side of the specimen represented in fig. 4. 
Fig. 6. Ventral view of the same, showing the depth of the shell, and the sinistrally coiled volutions. 
Platyceras Ammon. 
Page 20. 
Fig. 7. View of an individual of medium size, showing the strong volutions and the peculiar lamellose 
structure. Port Colbome, Canada. 
Figs. 8, 9. Views of the opposite sides of a large individual, showing the general form of the shell. Darien, N. Y. 
Fig. 10. Ventral view of the specimen figs. 8 and 9, showing the enrolling of the beak which in the figure is 
represented as too nearly on the same plane; it is directed more upwards, leaving a greater 
depth of the outer volution on the lower side. 
