PLATE 13. 



Page 



Figs. 1-5. Strophodonta patersoni 89 



1. A ventral valve, of medium size, and depressed convex form. 



2. A larger imperfect specimen, showing more distinctly the transverse wrinkles.' 



8. A large individual in which the strias are not so .strongly marked as in the other specimens. 

 4. A cast of the ventral valve, showing the muscular impression, and preserving the marks of the 



exterior strire. 

 6. A profile of fig. 8. 



Figs. 6-11. Strophodonta inequiradiata ;... . 87 



6. A ventral valve of an individual of medium size. 



7. A larger individual, having the cardinal extremities produced. 



8. A cast of a large ventral valve. 



9. A profile of fig. 8. 



10. The cast of a ventral valve of this species. 



11. An enlargement of the muscular impression of the same specimen. 



Figs. 12, 13. Strophodonta hemispheric a 90 



12. A ventral valve of e.xtremely gibbons form, from Poil Colbome, Canada West. 

 18. A profile of the same. This specimen presents some variations from the usual form and 

 character of those from New York and Ohio, which have been referred to this species. 



