﻿24 TRUNCILLA 



Ufiio capillaris Lea, Trans. Am. Phil. Soc, V, 1834. p. 29, pi. 



II, fig. 2 ; Obs., I. 1834, p. 141, pi. II, fig. 2. 



The male shell of this species resembles closely in form those 

 of certain species of Pleiirobcrna such as P. edi^arianum or 

 P. dolahcUoidcs. The marsupial swelling of the female is 

 rather small, it does not differ much in texture from the rest of 

 the shell and is not separated from it by sulci, being merely 

 a gradual inflation. 



(jroup of TruncUla pcrplcxa. 



Shell of the male with median and posterior radiating ridges, 

 both of -which are usually somewhat nodose, post-basal expan- 

 sion of the female rounded, large, thin, placed far back. 



Truncilla PERi'LEXA (Lea), 



Shell solid, subinflated, inequilateral, irregularly ovate, ellip- 

 tical or obovate ; beaks full, somewhat turned forward over a 

 small lunule; surface with irregular growth lines, with a radial 

 row of knobs running down near the middle of the disk and 

 sometimes with others on the low, narrowly rounded posterior 

 ridge ; epidermis tawny or yellowish-green, feebly rayed, 

 smooth and shining; pseudocardinals triangular, double in 

 the left valve, triple in the right ; muscle scars well impressed ; 

 nacre white to salmon red. Male shell generally irregularly 

 ovate with a deep, rather wide radial groove behind the row 

 of nodules or knobs, ending in a sinus, the hinder end bluntly 

 pointed. Female shell generally obovate, larger than that of 

 the male, having an enormous, flattened, rounded marsupial 

 swelling extending from the middle of the base to near the 

 upper part of the posterior end, this being thin and usually 

 dark green ; posterior muscle scars large, impressed. 



Length (male) 50, height 37, diam. 2^ mm. 



Length (male) 58, height 41, diam. 26 mm. 



Length (female) 87, height 57, diam. 36 mm, 



Ohio River drainage; southern Michigan? 



Type locality, Ohio River. 



