PLATE 6:3. 



Paec 



Fi2. 1, 2, 3. Platvceras lamkllosum. 330 



1 a, b. The anterior and posterior sides of a Kmall specimen. 



1 c. Knlargement of the surface, showing the undulating transverse lamella! and the fine lon- 



gitudinal striic. 



2 a. b. A'iews of the anterior and posterior sides of a larger individual. 



3. A larger individual, in which the transverse lamella; are mucli subdued : the longitudinal 

 ridge is an accidental feature. 



Fig. 4-9. Platyceb.\s spirale. 331 



4. A young individual of this sijccies, 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. 



6. A specimen of equal size with the preceding, in which the pl'cations are hut partially 



developed, or shown principally in the undulations of the stria; 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 off, 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 e.xpansion towards the aperture is increased beyond 

 the natural width, by compression. 



Fig. 10, 12 & 13. Platyceras incii.e. 332 



10. The lower part of the shell, consisting of a single volution. 



12. A s])ccimen 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. li 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;. 



