PLATE 16. 



Page 



Fig. 1 - 8, & 16. Stkophodonta varistriata. 180 



1 o. A young individual sliglitly convex in the centre towards the heak, and flat at the sides. 

 1 b. Profile showing tlie outline from beak to base. 



1 c. Enlargement showing the stronger elevated strise with the finer intermediate ones, and the 

 commencement of other stronger ones in the midst of the finer striae. 



2. An individual of the same character, having a greater convexity near the beak. 



3 o. A similar form where the beak or umbo is not elevated, and the whole shell nearly flat. 



3 b. Profile showing the curvature of the shell near the base. 



3 c. Enlargement of striae, showing the fasciculate character. 



3 d. A farther enlargement of the surface, showing the concentric striae. 



4 a. An individual having the character of S. rectilateris. 

 4 b. Profile of the same. 



4 c. Profile of an individual having similar characters of surface, with a greater convexity. 



4 d. Enlargement of striae of 4 a, showing the alternating size and frequent bifurcation. 



5 o. The S. impressa of Conrad, natural size. 



5 b. Profile of same, showing the abrupt bending or geniculation towards the base. 



5 c. Enlargement of striae, showing the coarser ones with intermediate fascicles of .smaller 

 ones. 



5 d. A portion of the surface enlarged where partially exfoliated on an impression of tlie 



exterior surface, showing the impressed lines made by the stronger striae; which is mere- 

 ly a reverse of fig. 5 d, or of fig. 3c & 3 d. 



6, An individual with coarser stria; than usual, the surface partially exfoliated, and profile of same. 



6 a. The striae enlarged, showing the punctate character of the surface when partially exfoliated. 



7 a, b. Illustrations of the surface of " Lepteena indent a" . 



8 o, c. Illustration of the hinge-line, area, vascular impression, etc. of the ventral valve, show- 



ing the apparent foramen, which is due to fracture , and has not the regular triangular form 

 of Strophornena. 



8 b. Enlargement of hinge-line, teeth, etc. of the dorsal valve. 



16. S. varistriata, var.arata. 



Fig. 9 - 12. Steophodonta planulata. 184 



9 a. An individual of medium size, with the hinge-extremities salient. 



9 b. Profile view of the same. 



9 c. Enlargement of the surface, showing the character of the radiating and concentric striae. 



10. An individual showing some faint concentric undulations. 



11 a. A large individual nearly entire, having the exterior surface slightly weathered, and 

 showing the puncta along the striae. 



11 6. Profile of the preceding specimen. 



11 c. Entargeraent of the surface, showing the character of the striae and arrangement of the 

 puncta. 



12. An individual in which the shell is partially removed, showing obscurely the form of the 

 vascular impressions. 



Fig. 13 - 15. Strophomena conradi. 194 



13 a. The ventral valve. 14. Profile view of the same. 



15. Ventral view of another individual. 



