PLATE XLVIII. 



PAGE. 



Figs. 1-3. Byssonychia alveolata, n. sp 631 



Three views of a right valve of this species. In two of the views the opposite 

 valve is restored except the radii. Middle beds of the Cincinnati group, Cin- 

 cinnati, Ohio. 

 Figs. 4-6. Allonychia ovata, n. sp 641 



4. A valve, somewhat weathered, showing, however, all the essential features of the 



species. Middle beds of the Cincinnati group, Covington, Kentucky. 



5. The upper part of an inner view of the same specimen, showing the high ligamen- 



tal area and o'.her characters. 



6. Anterior view of same. 



Fig. 7. Allonychia Jamesi, Meek, sp 641 



An excellent cast of the interior of a right valve of this species. Middle beds of the 

 Cincinnati group, Cincinnati, Ohio. 



Figs. 8-9. Allonychia subrotunda, n. sp 642 



Lateral and anterior views of the specimen described. Middle beds of the Cincin- 

 nati group, Cincinnati. Ohio. 

 Figs. 10-11. Ctenodonta cingulaTa, Ulrich 680 



10. Exterior of a silicified right valve. 



11. Interior of same, x 2. 



Fig. 12. Cycloconcha mediocardinalis, Miller 6S6 



A right valve showing the hinge. Lower beds of the Cincinnati group, Cincinnati, 

 Ohio. 



Figs. 13-14. Cycloconcha ovata, n. sp 687 



13. A finely preserved left valve. 



14. Hinge of a right valve, x 2. 



15. Hinge of a left valve, x 2. Lower beds of the Cincinnati group, near Cincinnati, 



Ohio. 



