﻿TRUNCILLA 5 



Shell snbtrapezoid, obliquely truncate below the posterior ridge, 

 base line shorter than dorsal line. 

 Radial depression narrow ; beaks far in front. T. sulcata. 

 Radial depression wide ; beaks not at front end. 



T. sampsonii. 

 Shell irregularly elliptical or oval. 



With a median row of knobs. T. perplexa. 



Without knobs. 



Subsolid. T. capscuformis. 



Solid. With a strong biangulate posterior ridge. 



T. Uorentina; hiemarginata. 



Subgenus Truncilla s. s. 



Shell covered with broken rays, somewhat triangular, and 

 without a wide, radiate, posterior furrow. 



Group of Truncilla triquetra. 



Shell greatly inflated, sharply truncate posteriorly; inflation 

 of the female shell at extreme post-basal point. 



Truncilla triquetra Rafinesque. 



Shell long triangular, much inflated, solid, slightly inequi- 

 lateral ; beaks full and high, turned inward and forward over 

 a well-marked lunule ; surface with irregular growth lines, 

 the dorsal slope being radially sculptured ; posterior ridge high, 

 angled; epidermis tawny to yellow-green with broken, bright 

 green rays and rows of green mottlings ; teeth subcompressed ; 

 pseudocardinals ragged, there being usually two in each valve ; 

 laterals short, elevated, granular, two in the left valve and one 

 in the right; beak cavities deep; anterior scars deep; nacre 

 white, silvery, thicker in front. Male shell much larger than 

 that of the female, less sharply triangular. Female shell having 

 the marsupial region elevated into a narrowly rounded, radially 

 sculptured ridge, projecting but little below the base. 



