PLATE 81. 
Fig. 1. 351. 11. MopioLopsts MopIoLaRis. (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. 
1b. Another specimen preserving the two valves, which are laterally compressed. The anterior extremities 
are narrowed, and somewhat obtusely pointed. 
1c. A single valve, with the posterior extremity more regularly rounded, and the hinge-line curved. 
1d. A smaller and shorter specimen, with the base not contracted or arched. 
1 e. A small specimen, contracted at the anterior, and expanded towards the posterior extremity. The base is 
arched, and the hinge-line apparently curved. 
1 f. 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. MopioLopsis NAsuUTUs. (Pag. 296.) 
Fig. 3. 352. 12. MopioLorsis TRUNCATUS. (Pag. 296.) 
3 a. View of the right valve of this species. 
3b. Profile view, one valve being more compressed than the other. y 
Fig. 4. 353. 13. Moproxopsis curta. (Pag. 297.) 
A large individual of this species, from near Grimsby, Canada West. 
Fig. 5. 354. 14. Mopiotopsis (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, 6, on some of the plates.) 
