﻿MARGARITANA 523 



iior high, their sculpture not made out ; hinge Hne sinuous, be- 

 ing incurved in front of the beaks ; posterior ridge angulated, 

 ending in a point behind at the base of the shell ; surface with 

 rude, uneven growth lines, brownish or yellowish-green, faint- 

 ly rayed, dull and dirty ; left valve with an imperfect, somewhat 

 double pseudocardinal, and two feeble, curved laterals ; right 

 valve with two small pseudocardinals and an imperfect lateral ; 

 anterior scars slightly roughened ; posterior scars elliptical ; 

 nacre purplish-tinted, rather bright, with a few pits. 



Length 84, height 42, diam. 18 mm. 



Type locality, Alabama. 

 Unio decumbens Lea, Pr. Ac. N. Sci. Phila., V, 1861, p. 40; 



Jl. Ac. N. Sci. Phila., 1862, p. 87, pi. xii, fig. 236; Obs., VIII, 



1862, p. 91, pi. XII, fig. 236. — vSowERBY, Conch. Icon., XVI, 



1868, pi. Lxxxii, fig. 432. 

 Margaron (Unio) decnuihens Lea, Syn., 1870, p. 62. 

 Margaritana decumbens Simpson, Syn., 1900, p. 679. 



Quite different from the other species, yet having the char- 

 acters of a Margaritana. It is a little strange that only the 

 type is known of this curious compressed, rather thin, trape- 

 zoidal species. 



Group of Margaritana hembeli. 

 Shell having its posterior part more or less corrugated. 



Margaritana hembeli (Conrad). 



Shell oblong, obovate to subrhomboid, sometimes a little 

 arcuate, subsolid to solid, inequilateral ; beaks moderately full, 

 their sculpture not seen ; posterior ridge low. rounded or some- 

 what double : anterior end rounded or subtruncate ; posterior 

 end feebly pointed below the median line and sometimes an- 

 gled at the base ; surface with rude, uneven growth lines ; pos- 

 terior end with more or less distinctly marked corrugated sculp- 

 ture, often divaricately plicate ; epidermis tawny-brownish or 

 blackish ; left valve with two low, stumpy, rough pseudocardi- 

 nals and two remote, feeble laterals ; right valve with one pseu- 



