﻿14 TKUNcn.r.A 



end of iS^i. and acknovvlcd<];'C(l by correspondents as received 

 that year (Bib. of publications of Lea, 1885, p. 3). As I am 

 not able to say which has precedence, I prefer retainin"^ the 

 well-known name of Lea rather than that of Say, which is less 

 known. 



Subgenus Scalknaria (Rafinesque, 1820) Agassiz. 



Scalenaria Rafinesque, Am. Gen. Sci. Phys. I'.rux., xiii, 1820, 



p. 309. — Agassiz, Arch, fiir Xaturg., I, 1852, p. 43. 



Male shell having a wide, radiating, shallow depression in 



front of the posterior ridge ; that of the female having a small, 



rounded, well-defined, radial post-basal swelling. Animal with 



marsupium occupying the greater part of the outer branchiae ; 



mantle enlarged below ; branchial opening with few papillae. 



Type: Unio sulcntus Lea. 



Group of TrunciUa sulcata. 



Shell elliptical, beaks high and well forward ; male shell not 

 radiately striated posteriorly. 



Truncii.i.a sulcata (Lea). 



Shell subquadrate or subtrapezoid, inflated, solid, very in- 

 equilateral ; beaks somewhat elevated, prominent, their sculp- 

 ture consisting of a few faint corrugations, -which are some- 

 times broken or are occasionally doubly looped ; lunuk distinct, 

 extending under the beAks ; surface nearly smooth or irreg- 

 ularly concentrically sulcate ; pseudocardinals subtriangular, 

 elevated, ragged, two in the left valve, one to three in the 

 right ; laterals granulate, double in the left valve, partly double 

 in the right ; beak cavities rather shallow ; muscle scars im- 

 pressed ; nacre purplish to deep purple, sometimes white. Male 

 shell much larger than that of the female, usually somewhat 

 trapezoid, the dorsal and basal lines lightly curved, the anterior 

 end squarely subtruncate, the posterior end pointed bluntly 

 above, slopingly truncate below, having a M-idely separated pair 

 of posterior ridges, often with a radial sulcus between. Fe- 

 male shell subquadrate, the hinder end radially sculptured and 



