DESCRIPTION OF 



PLATE III. 



Page 



Fig. 1 & 2. STROPHODONTA ARCTJATA. 492 



1 a, 6, c. Dorsal, ventral and profile view of a specimen : natural size. 



2 a. Interior of ventral valve, showing the muscular and vascular impressions, the central 



cardinal process, and the indentations of the area made by the cardinal process of the 

 opposite valve. 



2 b. A portion of the same enlarged, showing the parts described. 



2e,/. Enlargement of the strise from two specimens, showing in 2/ the prevailing character, 

 while some specimens present the features of 2 e. 



Fig. 3. STROPHODONTA LEPIDA. 493 



3 a. Exterior view of a ventral valve of large size. 



3 b. Interior of the ventral valve, showing the muscular and vascular impressions. 



3 c. Interior of a dorsal valve, showing the crenulated hinge line and muscular impressions. 



Fig. 4. STROPHODONTA REVERSA. 494 



4 a. Dorsal view of a specimen having the margin somewhat irregularly plicated, which is 



apparently due to accident during the life of the animal. 

 4 b. Ventral view of the same. 

 4 c. Profile view. 



4 d. Interior of ventral valve, showing the indented margin of area, bilobed cardinal process, 



the muscular and vascular impressions. 



Fig. 5. STROPHODONTA DEMISSA. 495 



5 a, 6. Ventral and dorsal views of a specimen of ordinary form and size, from Iowa. 

 5 c. A specimen where the cardinal extremities are more salient. 



5 d. Profile, showing the convexity of the specimen. 



5 e. Interior of the ventral valve of a specimen from New-York, showing the bilobed cardinal 

 process in the centre of the area, and the muscular end vascular impressions. 



5f. Enlargement of the area surface, showiug the deeply striate character. 



5 g. Interior of the dorsal valve of a specimen from New-York, showing the muscular im- 

 pressions and the double cardinal process. 



5 h. The same enlarged, showing the crenulate dental lamella on each side of the base of the 

 cardinal process. 



5 i. Enlargement of a portion of the area and cardinal process of the dorsal valvej looking 



from the outside. In this individual there are no prominent crenulated lamellte, as in fig. 5 h. 

 5k. A similar view of another individual, showing, at the base of the cardinal process, the 

 indentations made by the two lobes oi the process from the ventral valve, and the lateral 

 crenulated lamellae. 



Fig. 6. STROPHODONTA FRAGILIS. 496 



6 a. View of the ventral valve. 



6 b Interior of ventral valve, showing the foliate vascular impressions, entire area, etc. 



6 e. Enlargement of the stria3. 



Fig. 7. PRODUCTUS DISSIMILIS. 497 



7 a, b. Dorsal and ventral views of the shell. 

 7 c. Profile of the same. 



7 d. Enlargement of the striae from the surface of the ventral valve. 



7 e. Enlargement of concentric striae from the surface of the dorsal valve. 



Fig. 8. PRODUCTUS PYXIDATUS. 498 



8 a. Ventral valve, showiug a few spiniferous tubercles on the upper part of the valve, while 



the ridges which usually characterize the lowi-.r part in such specimens are not percepti- 

 ble. This specimen is proportionally narrower than the prevailing forms. 



8 b. Ventral valve of the ordinary form, without spiniferous nodes or ridges. 



8 c. Dorsal valve of another individual, with some undefined radiating ridges upon the surface. 



8 d. Profile view of a specimen. 



S e. Interior of a dorsal valve, showing the cardinal process, muscular impressions, etc. 



Fig. 9. PRODUCTUS SHUMARDIANUS. 499 



9. Interior of a dorsal valve, showing the marks of the spiniferous ridges upon the inner sur- 

 face. 



Fig. 10. PRODUCTUS SUBALATUS. 500 



10 a. Ventral valve of a specimen of medium size, with few spines, and preserving the usual 



characteristics of the species. 



10 6. Ventral valve of a larger specimen, showing the irregular distribution of the spines. 

 10 c. Profile view of fig. 10 b. 



