﻿C6 TRUNC1I,I,A 



and in that state is often somewhat cloth-like. With ag^e the 

 shell usually becomes brownish and the rays are less conspic- 

 uous. The hinder part of the male shell is sometimes slightly 

 radially sculptured. 



Var. delicata Simpson. 



Shell more delicate than the type, smaller, paler colored, 

 that of the male (the only one I have seen) being somewhat 

 drawn out and pointed behind. 



Length (male) 44, height 31, diam. 24 mm. 



Type locality, Detroit River, Michigan. 

 Tnincilla sulcata var. delicata Simpson, Syn., 1900, p. 520. 



Mr. Bryant Walker sent me specimens of a form, which I 

 refer to this species, but which is smaller and in every way 

 more delicate. I propose the above varietal name for it. It 

 is no doubt derived from the typical T. sulcata but, owing to 

 different environment, has changed considerably. 



Group of Truncilla haysiana. 



Shell shining, round-oval ; posterior part of both male and 

 female distinctly radially sculptured. 



TrunciIvLA haysi.'\na (Lea). 



Shell short, subtriangular to suborbicular, inflated, solid, in- 

 equilateral ; lunule variable in size ; beaks full and high, with 

 feeble sculpture ; surface with irregular, concentric sculpture, 

 the anterior half of the shell rather smooth, the posterior half 

 with radial, subnodulous sculpture, there being a shallow radial 

 furrow in front of the posterior ridge ; epidermis tawny to 

 chestnut, shining on the front half of the shell, rough and 

 often lighter colored behind ; pseudocardinals stumpy, triangu- 

 lar, ragged, double in the left valve, partly double in the right ; 

 beak cavities shallow ; muscle scars well impressed ; nacre pur- 

 ple 01 white, male shell larger than that of the female, subtri- 

 angular. Female shell rather small, suborbicular; marsupial 

 swelling raised but slightly, having a sharp ridge on its an- 

 terior part, thinner and somewhat excavated within ; hinder 

 muscle scars large and deep. 



