﻿TRUNCILLA 7 



consisting of broken, somewhat; doubly-looped ridges. The 

 edges of the shell at the marsupial region are sometimes 

 toothed and gape slightly. 



Group of Trvmcilla brevidens. 



Shell somewhat quadrate, not sharply truncate behind ; post- 

 basal swelling of female in front of post-basal point and 

 rounded below. 



Truncilla brevidens (Lea.) 



Shell subquadrangular or subrhomboid, very solid, inflated 

 when old, somewhat inequilateral; beaks much elevated, the 

 umbonal region being elongated and flattened, the sculpture 

 feeble, doubly-looped bars ; posterior ridge well developed, nar- 

 rowly' rounded ; surface with irregular growth lines with light 

 radial sculpture behind ; epidermis yellowish, tawny or tawny- 

 brown with narrow, broken, radial markings, somewhat cloth- 

 like; pseudocardinals ragged, generally double in each valve; 

 laterals very short, heavy, strongly obliquely sculptured, double 

 in the left valve and single or semi-double in the right ; anterior 

 scars small, deep; posterior scars large, deep; nacre white, 

 silvery; beak cavities shallow. Male shell rhomlboid or sub- 

 triangular in outline, moderately inflated, flattened on the disk. 

 Female shell subquadrate, rounded behind, greatly inflated; 

 marsupial swelling narrow, elevated, rounded, ridged, toothed 

 below and marked with the remains of former teeth, separated 

 decidedly from the rest of the shell, thinner and showing its 

 position within by a rounded radial furrow ; posterior muscle 

 scars large, enormously deep. 



Length (male) 83, height 63, diam. 42 mm. 



Length (female) y^, height 55, diam. 50 mm. 



Tennessee drainage. 



Type locality, Ohio. 

 Unio brezndens Lea, Trans. Am. Phil. Soc, IV, 1834, p. 75, 



pi. VI, fig. 6 ; Obs., I, 1834, p. 85, pi. VI, fig. 6.— Hanley, Biv. 



Shells, 1843, P- 19S, pi. XX, fig. 41.— Chenu, 111. Conch., 



1858, pi. VIII, figs. 6, 6a, 6b. 



