PLATE 81. 



Fig. 1. 351. 11. MODIOLOPSIS MODIOLARIS. (Pag. 294.) 



1 a. A specimen preserving the two valves in connection, showing the hinge-line, and the anterior muscular 

 impression, which produces an elevation upon the outer surface of the shell. 

 ' 1 b. Another specimen preserving the two valves, which are latei-ally compressed. The anterior extremities 

 are narrowed, and somewhat obtusely pointed. 



1 c. A single valve, with the posterior extremity more regularly rounded, and tlie hinge-line curved. 



1 rf. A smaller and shorter specimen, with the base not contracted or arched. 



1 €. A small specimen, contracted at the anterior, and expanded towards the posterior extremity. The base is 

 arched, and the hinge-line apparently curved. 



ly. A specimen from the shales at Madison (Indiana), preserving both valves. 



1 g. The anterior extremity of a cast of this species, showing the prominence of the muscular impression. 



Fig. 2. 203. 4. MoDioLOPSis nasutus. (Pag. 296.) 



Fig. 3. 352. 12. MoDioLOPsis truncatus. (Pag. 296.) 



3 a. View of the right valve of this species. 



3 b. Profile view, one valve being more compressed than the other. 



Fig. 4. 353. 13. Mobiolopsis ctjrta. (Pag. 297.) 



A large individual of this species, from near Grimsby, Canada West. 



Fig. 5. 354. 14. M.omoh07Bis (Species undetermined). (Pag. 297.) 



5 a. Left valve of the fragment. 5 6. Dorsal view of the same. 



(This species is erroneously marked 4 a, b, on some of the plates.) 



