﻿12 'J'lUINCILI.A 



Unio Icnior Lha, Tr. Am. Phil. Soc, VI IT, 1843, P- 204, pi. 



XII, fig. 18; Obs., Ill, 1842, J). 42. pi. XII. fi.u- 18. — CiiENU, 



111. Conch., 1858. })1. XXVII, figs. 4, 4a. 4/'. — RiCEV% Conch. 



Icon., XVI, 1864, pi. XVII, fig. 75. 

 Margaron (Unio) lenior Lea, Syn., 1852, p. 39; 1870, p. 62. 

 TrnnciUa lenior Simpson, Syn., 1900, p. 518. 



I have only seen female shells of this species, which seems 

 to be distinct from all others. Its delicate, almost thin, struc- 

 ture will at once distinguish it, as well as the decided sulcus 

 behind separating the marsupial swelling from the rest of the 

 shell. Unfortunately I have never seen a male shell. 



Lea changed his name lenis to lenior, probably because Con- 

 rad had previously used the fomier for a species of Unio, 

 which is no doubt a young vcntricosa. 



Group of TrnnciUa arcceformis. 



Shell greatly inflated, with a sharp posterior ridge, and two 

 lesser ridges above it ; inflation of the female flattened on its 

 base. 



TrunciIvIvA arc^formis (Lea). 



Shell usually subquadrate or subrhomboid in outline, very 

 solid, greatly inflated, inequilateral ; beaks very full and high, 

 in contact with each other, their sculpture very faint ; posterior 

 ridge full and high, generally double, subangulate, behind 

 which the shell is subtruncate ; surface with irregular growth 

 lines ; epidermis tawny to yellowish-green, feebly rayed, more 

 or less cloth-like ; lunule small ; pseudocardinals small, stumpy, 

 rough, two in the left valve, one to three in the right ; laterals 

 short, elevated, often somewhat vertically striate ; anterior 

 scars small, deep ; posterior scars shallow in the male shell, 

 impressed in that of the female ; nacre white, thickened in 

 front. Male and female shells considerably alike in outline, 

 those of the latter less elevated, having a high, rather wide 

 marsupial swelling, which is flattened below and docs not pro- 

 ject below the base line and has radial, faint sculpture toothed 



