﻿520 MARGARITANA 



but the epidermis is more dull black, the beaks are usually 

 higher and more strongly developed, the nacre is white, and 

 it has fairly well-developed laterals. European conchologists 

 seem to have quite commonly mistaken heavy, large forms of 

 Unio batazms for Retzius' species, and in a number of cases 

 the M. margaritifera has been taken for it. 



Ortmann, (1. c), follows Kobelt, (Nachr. Bl. D. Ges., 1909, 

 p, 43), in referring Unio crassus Retz. to the species commonly- 

 known as Unio bataz'us. 



Haas, (Nachr. Bl. D. Ges., 1910, p. 181), has recently made 

 this species the type of a new genus, Pseudiinio, but, apparent- 

 ly, without sufificient reason. 



Margaritana i.aosensis (Lea). 



Shell elongated, arcuate, rather solid, not inflated, inequilat- 

 eral ; beaks slightly elevated, not full, their sculpture consist- 

 ing of ridges that nearly follow the growth lines ; posterior 

 ridge high, very v.ide and rounded ; anterior end of the shell 

 rounded, posterior end a little wider, rounded or feebly point- 

 ed ; surface with rude, concentric growth lines ; epidermis 

 brownish-green or greenish-brown and subshining in young 

 shells, brown or blackish and dull in old ones ; left valve with 

 two small, stumpy pseudocardinals, the anterior one often al- 

 most obsolete, and two remote, small laterals ; right valve with 

 two pseudocardinals, the hinder rudimentary and one lateral ; 

 laterals granular and showing traces of vertical striation ; mus- 

 cle scars well impressed, the anterior ones rough, the posterior 

 elliptical ; nacre whitish or purplish, thickened in front, gener- 

 ally showing small pits. 



Length 90, height 37, diam. 22 mm. 



Laos Mountains, Cambodia; Siam; Burma. 

 Unio laosensis Lea, Pr. Ac. Nat. Sci. Phila., VII, 1863, p. 190; 



Jl. Ac. N. vSci. Phila.. VL 1866, p. xxi, fig. 61 ; Obs., XI, 



1867, p. 67, pi. XXI, fig. 61. — SowERBY, Conch. Icon., XVI, 



1866, pi. xi.vii, fig. 256. 

 Marf^aron (Unio) laosensis Lea, Syn., 1870, p. 62. 

 Margaritana laosensis Simpsox, Syn., 1900, p. 678. 



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