THE NAUTILUS. 13 



dium size. Although the characteristic color of the epidermis is 

 gone, these specimens agree completely with this species in the shape 

 of the shell and of the liinge teeth. 



This species is found in the Cheat River and elsewhere in western 

 Pennsylvania, preferring smaller streams. 



6. Lampsilis ligamentina (Lam.). 4 isolated valves; one young, 

 the others of medium size. 



At present in the Cheat River, but not abundant. It is the most 

 abundant species in the large rivers of western Pennsylvania. 



7. Obovaria circuhis (Lea). 1 left valve; small. Not typical, 

 inclining toward 0. lens (Lea) in shape; probably a female. 



This species (including the form lens) is found scattered over the 

 Ohio drainage in western Pennsylvania. From the Monongahela it 

 is known only from a single locality at Charleroi, Washington 

 CouDty, about 35 miles north of Point Marion 



8. Cyprogenin irrorata (Lea). 2 double, 4 isolated valves, of 

 medium size. 



Not in the Monongahela drainage, and altogether rare in western 

 Pennsylvania; known from the Ohio below Pittsburg and from the 

 Allegheny River in Allegheny and southern Armstrong County. 

 No live specimens have been found recently. 



9. Ptychobranchus phaseohis (Hildr.). 1 double, 3 isolated valves, 

 of medium size. 



Abundant in Cheat River; also in Dunkard Creek. Widely dis- 

 tributed in the Ohio drainage in western Pennsylvania, with excep- 

 tion of the large rivers. 



10. Unio gibbosus Barn. 4 double, 7 single valves, medium and 

 small size. 



Abundant in Cheat River; also in Dunkard Creek. Everywhere 

 in western Pennsylvania. 



11. Unio crassidens Lam. 7 double, 4 single valves; one above 

 medium size, the others medium and small. 



Only in the large rivers; abundant in the Ohio and lower Alle- 

 gheny. Known from the Monongahela at Charleroi, Washington 

 County, but not farther up. No trace of it in the Cheat. 



12. Pleurobema clava (Lam.). 2 single valves, medium size. 

 Present in Cheat River. A rare species in western Pennsylvania, 



preferring smaller streams. 



13. Quadrula tubrotunda (Lea). 1 double, 5 single valves; me- 

 dium and small size. 



