PLATE 6:). 
Page 
Pig. 1, 2, 3. Platyceras lamellosum. 330 
1 a, b. The anterior and posterior sides of a small specimen. 
1 c. Enlargement of the surface, showing the undulating transverse lamella' and the fine lon¬ 
gitudinal strife. 
2 a , b. Views of the anterior and posterior sides of a larger individual. 
3. A larger individual, in which the transverse lamella' are much subdued : the longitudinal 
ridge is an accidental feature. 
Fig. 4-9. Platyceras spirale. 331 
4. A young individual of this species, in which no plications arc developed. 
5 a. A larger specimen, in which the plications are very strongly developed on the right po¬ 
sterior side of the shell. 
5 b. The posterior side of the same shell. 
G. A specimen of equal size with the preceding, in which the plications are hut partially 
developed, or shown principally in the undulations of the striae of the surface. 
7. A similar specimen which is smooth on the anterior side, and showing only two or three 
plications on the posterior side. 
8. A more elongated specimen, with strongly developed plications. ( The upper part has been 
broken oil', and presents some imperfection at the junction of the two parts.) 
9 a. The anterior side of another specimen, in which plications are but faintly developed. 
9 b. The posterior side of the same. The expansion towards the aperture is increased beyond 
the natural width, by compression. 
Fig. 10, 12 & 13. Platyceras incile. 332 
10. The lower part of the shell, consisting of a single volution. 
12. A specimen preserving imperfectly the apex and nearly two volutions below. The specimen 
is somewhat flattened from pressure. 
13. A fragment which is probably the apex of a specimen of this species. 
Fig. 11. Platyceras tub.eforme. 332 
11. A fragment preserving a little more than one volution. 
Fig. 14 a - e . Platyceras newberryi. 333 
14 a. Dorsal side of the last volution. 
14 b. View of the top of the spire. 
14 c. The lower side of the shell. 
14 d. Posterior view, partially showing the aperture. 
14 e. Enlargement of the surface, showing the longitudinal stria;. 
