﻿8 TRUNCILLA 



Margarita (Uriio) bre^idcns LE/\. Syn., 1836, p. 29; 1838, p. 21. 

 Margaron (UnioJ hreindcns Lka, Syn., 1852, p. 32; 1870, p. 50. 

 Truncilla brevidens Simpson Syn., 1900, p. 517. 

 Unto interruptus Conrad, New F. W. Shells, 1834, p. 69; 



Monog., X, 1838, p. 88, pi. xlviii. — Kuster, Conch. Cab. 



Unio, 1861, p. 182, pi. i.vii, fig. 3; pi. Lx, fig. 2. — Reeve, 



Conch. Icon., XVI, 1864. ]>]. xiv, fig. 56. 



A large ponderous species having, when unworn, a more 

 cloth-like surface than T. triquetra. The female shell is more 

 quadrate than that of the male ; it is more inflated and from 

 the material I have been able to examine should judge that it 

 is usuallv a little smaller. Most specimens are smaller than 

 those whose measurements I have given, which are from the 

 Lea collection. Until the male shell is nearly full grown it 

 is scarcely inflated. The marsupial area of the female is very 

 distinctly marked off from the rest of the shell by sulci, and 

 its outline on the base of the shell is semicircular. It pro- 

 jects well below the rest of the base. 



Truncilla penita (Conrad.) 



Shell solid, rhomboid or subtriangular. somewhat inequi- 

 lateral ; beaks full, elevated ; surface with irregular growth 

 lines, the posterior end being radially sculptured ; epidermis 

 yellowish, greenish-yellow or tawny, sometimes with incon- 

 spicuous dots or arrow-head markings of darker color arranged 

 radially on the posterior part ; pseudocardinals ragged, irreg- 

 ular, two in the left valve and three usually in the right ; lat- 

 erals short, double in the left valve, partly double in the right ; 

 beak cavities shallow ; muscle scars impressed, the posterior 

 ones in the female shell large and deep ; nacre white or straw- 

 color. Male shell much larger th^n that of the female, higher 

 in proportion to length, more inflated, subtriangular. Female 

 shell long rhomboid, smaller and less solid than that of the 

 male ; marsupial swelling rather large, radially grooved, pro- 

 jecting back behind the rest of the shell and below the base 

 line, thinner and excavated within. 



