﻿NEPHRONAIAS 283 



of the marsupium. There is a shell in the National Museum 

 collection from Belize, which is probably a male of this species, 

 which is a little shorter than Kuster's figure, is more distinctly 

 biangulate behind, and has a nearly straight base line. x\n- 

 other shell in the Lea collection from Honduras I would refer 

 to this. It is a male and has salmon and purple-tinted nacre 

 and seems to stand between plicatula and tahascoensis. In- 

 deed I think it quite probable that the two species mentioned, 

 Lea's Unio persitlcatus and Charpentier's rugulosus are all 

 forms of one species varying a little in form, color of nacre 

 and epidermis, and in the position of the beaks. 



Nephronaias rav]STElla (Morelet). 



Shell small, inequilateral, subrhomboid, rather compressed, 

 strongly concentrically striated; beaks apparently low, their 

 sculpture not seen ; epidermis brown ; left valve with two solid 

 pseudocardinals and two laterals; right valve with two pseu- 

 docardinals and a single lateral ; anterior muscle scars deep, 

 semicircular; posterior scars suboval, well marked; nacre 

 whitish, tinted lead-color or yellowish-brown. 



Fischer and Crosse figure two shells, both badly eroded but 

 apparently having a double posterior ridge, which ends m a 

 distinct, wide biangulation behind. One of these shells is a 

 male and is decidedly arcuate on the base line, the lower part 

 of the biangulation being on the line of the base ; the other is 

 probably a female and has the base line curved and full be- 

 hind the middle, the base of the hinder biangulation being 

 slightly raised. 



Length 39, height 21. diam. 13.5 mm. 

 Guatemala ; Tabasco, Mexico. 

 Unio ravistellns Morelet, Test. Noviss., No. i, 1849, p. 29.— 

 KusTER. Conch. Cab. Unio, 1856. pi. xlii, fig. 6.— Sowerby, 

 Conch. Icon., XVI, 1868, pi. lxxii, fig. 366 ?— Fischer and 

 Crosse, Miss. Sci., 11, 1894, p. 609, pi. lxi, figs. 4. 5, and 

 5a.— VON Martens, Biol. Cent. Am., Moll., 1901, p. 5^6, pi- 

 xxxvrii, figs. 2-6a. 

 Margaron (Unio) raiistellus Lea, Syn., 1870, p. 40. 

 Nephronaias ravistellns Simpson, Syn., 1900, p. 597. 



