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nacre, while that of the last named species is bordered with 

 white. The shell figured by Conrad is probably a male. Ac- 

 cording- to Conrad its greatest diameter is at the middle of the 

 shell, and from that point it rapidly tapers toward each end. 



Conrad's figure is a poor one, and 1 can not be positive just 

 where the species should be placed, but incline to think it a 

 member of the texascnsis group. Lea has a shell, which he 

 calls the Unio puUus of Conrad, which came from Ravenel, 

 labeled "S. Carolina," but which. I think, is not this, but some 

 species of the siibrostrata group. It is f|uite probable that pidla 

 is the same as Lea's cori'uncula. 



Subgenus Proptrra Rafinesque. 1819. 



Proptera Rafinesque, Jl. Phys. Chim. Hist. Nat., LXXXVIH, 



1819, p. 426. — Simpson, Syn., 1900, p. 566. — Ortmann, 



Ann. Car. Mus., VIH, 1912, p. 339. 

 Metaptera Rafinesque, Ann. Gen. Sci. Phys. Brux., V, 1820, 



p. 299. 



Shell usually large, gaping at the anterior base and edge of 

 the dorsal slope, winged along the dorsal region when young 

 and often when adult ; beak sculpture feeble, consisting, when 

 developed, of an anterior and posterior loop, the former often 

 wanting ; the latter sometimes becomes slightly nodulous ; epi- 

 dermis generally brown, often cloth-like when fresh, rayless or 

 feebly rayed ; teeth rather compressed, pseudocardinals fre- 

 quently imperfect or nearly wanting ; laterals remote ; anterioi' 

 muscle scars often complicated ; dorsal scars consisting of a 

 row of from four to thirty distinct, often deep, impressions, 

 running from the cavity of the beak obliquely downward an- 

 teriorly ; nacre purplish. x\nimal with large branchiae ; mar- 

 supium consisting of numerous, generally fine, ovisacs, which 

 are often somewhat radial ; mantle thickened and distinctly 

 double on the border, often papillose behind, where the outer 

 fold develops into a thickened flap ; branchial opening with 

 irregular teeth ; anal opening smooth or only slightly crenulate 



Type, Unio alata Say. 



Ortmann, (1. c), raises this group to generic rank. 



