PLATE IvIV. 



PAGE 



Figs. 1-3. Ischyrodonta unionoides, Meek sp 677 



1. Interior of a large right valve showing the hinge and the anterior adductor and 



pedal muscle scars. Also the left side of an unusually well preserved cast of 

 the interior. 



2. Entire impression of the inner side of a right valve, showing the anterior muscular 



scar and the impression of the subcardinal rib that supported the internal 

 ligament. 



3. A testiferous example of a right valve of less regularly ovate shape than usual. 



Middle beds of the Cincinnati group, Covington, Kentucky. 



Figs. 4-9. ISCHYRODONTA modioliformis, n. Sp : 676 



4. Rather small example preserved in part as a mold of the exterior. In this specimen 



the outline, especially in the basal region, differs somewhat from the usual form 

 of the species. 



5. Sharply marked cast of the interior showing the muscular scars and the pallial line. 



6. The right side of a large and nearly perfect cast of the interior. 



7. Left side of a cast in which the hinge is longer than usual. 



8. Dorsal view of same. 



9. From a gutta percha impression of a natural mold of the exterior, showing the 



surface markings, x2, as they appear in the central part of the posterior half of 

 the left valve Upper beds of the Cincinnati group, Richmond, Indiana. 



FigS. 10-11. ISCHYRODONTA MISENERI, 11. Sp 675 



10. Antero-cardinal view of a testiferous specimen. 



11. Right side of same showing the usual size and form of this spicies. Upper beds 



of the Cincinnati group, Richmond, Indiana. 



Figs. 12-15/ Ischyrodonta ovaus, Ulrich : 674 



Four views of the original type of this species. Uppermost beds of the Cincinnati 

 group, near Richmond, Indiana. 



FigS. 16-19. ISCHYRODONTA DECIPIENS, 11. Sp 673 



16-18. Three views, respectively inner, antero-cardinal, and outer, of a nearly perfect 



.right valve. 

 19." interior of the largest left valve seeu. The specimen is slightly weatherworn. 

 Upper beds of the Cincinnati group, near Richmond, Indiana. 



FigS. 20-21. ISCHYRODONTA ELONGATA 675 



20. Small specimen preserved as a mold of the exterior. Upper beds of the Cincinnati 



group, Richmond, Indiana. 



21. Left side of the original type of the species. The specimen is an excellently de- 



fined cast of the interior, itom Oxford, Ohio. 



