PLATE LI. 



PAGE 



Figs. 1-3. Psilonychia perangulata, n. sp 649 



1. -Left valve with some of the test weathered away so that the posterior muscular 



impression is exposed to view. Middle beds of the Cincinnati group, Cincinnati, 

 Ohio. 



2. Anterior view of same. 



3. Hinge oi same. 



Figs. 4-5. Clionychia excavata, n. sp 651 



Lateral and anterior views of a cast of the interior The thickness of the specimen 



has doubtless been reduced by pressure and I believe to an amount not less - 

 than shown in figure 5. Upper beds of the Cincinnati group, Richmond, Indiana. 



Fig. 6. Pyrenomceus subcuneatus, n. sp '. 682 



A left valve of this species. Lower beds of the Cincinnati group, Covington, Kentucky. 



Figs. 7-8. Pyrenomceus decipiens, n. sp 681 



7. A good cast of the interior of a left valve, showing the usual form of casts and pre- 



serving more distinct traces of the muscular scars than any other specimen seen. 



8. Testiferous example. The raised line in the middle of the posterior cardinal 



slope is natural, but the concentric strise are too fine to be successfully repre- 

 sented of the natural size. Middle beds of the Cincinnati group, Cincinnati, Ohio. 



Figs. 9-10. Modiolodon 'Truncatus, Hall sp 656 



9. The left side of a cast of the interior belonging to the collection of Mr. George 



Asherman. This is the usual form of the species as it occurs in the middle beds 

 of the Cincinnati group near the tops of the hills at Cincinnati, Ohio. 



10. The right side of an internal cast of a variety occupying a higher position in the 



Cincinnati group, and found associated with the next species at Versailles, In- 

 diana. In this variety the anterior end is wider than in the more typical form 

 of the species represented in figure 9. 



Figs. 11-13. Modiolodon subovalis, n. sp 655 



11 and 13. The right side and a cardinal view of a good cast of the interior. 

 12. The left side of a larger cast of the interior. Upper beds of the Cincinnati group, 

 Versailles, Indiana. 



Figs. 14-21. Cycloconcha milleri, Meek sp 686 



14. A large right valve preserving faint radiating lines on the posterior cardinal slope. 

 15 and 16. Two views of a smaller testiferous example. 



17. The hinges of thiee small right valves, x2, showing a gradual change in the 



cardinal teeth with age. 



18. Hinge of a fully grown right valve x2. 



19-21. Hinges of three left valves, x2. Upper beds of the Cincinnati group, Ver- 

 sailles, Indiana. 



