﻿264 N'i:i'iii«i\\i.\s 



\'on MartCMis fij^urcs for the first time this hitherto ahnost 

 unknown s])ecies. 1 scarcely know wliere to pkice it, as it does 

 not have any very decided characters. It may be a male shell, 

 not quite mature, of the genus Ncphronaias, or it is possibly 

 a Unio and related to U. aratiis, thoug^h the form is quite dif- 

 ferent. 



Nephkonaias goascokanensis (Lea). 



Shell elongated, scarcely inflated, subelliptical to subtrian- 

 gular ; dorsal line curved gradually at the hinge and more sharp- 

 ly behind ; base line nearly straight in the male, curved outward 

 at the posterior base in the female shell ; posterior ridge low, 

 somewhat double ; beaks full, moderately high, their sculpture 

 consisting apparently of nearly concentric, fine ridges ; epider- 

 mis smoky-olive in the yoimger shells, dirty brownish in old 

 shells, slightly sulcate, rather smooth in young shells, scarcely 

 rayed even when young; left valve with two small pseudocar- 

 dinals, and two curved laterals ; right valve with one pseudo- 

 cardinal with a very small tooth above and one lateral ; mus- 

 cle scars well impressed, the anterior rough. 



Length 60, height 33, diam. 20 mm. 



Goascoran River. Honduras ; Tehuantepec ; Chiapas, Mexi- 

 co ; W. Guatemala; Estero Real, Nicaragua. 

 Unio goascorancnsis Lea, Pr. Ac. N. Sci., Phila., II, 1858, p. 



118; Jl. Ac. N. Sci. Phila., IV, i860, p. 258, pi. xu, fig. 139; 



Obs., VII. i860, p. 76, pi. xu, fig. 139. — VON Martens, 



Biol., Cent. Am., Moll., 1900, p. 501, pi. xxxviii, figs. 10, 



loa. 

 Margaron (Unio) goascorancnsis Lea, Syn., 1870, p. 45. 

 Ncphronaias goascorancnsis Simpson, Syn., 1900, p. 594. 

 Unio guatciiialanus von Martens, Biol. Cent. Am., Moll.,. 



1000. p. 519, pi. XXXVI II, figs. y-Sa. 



It is extremely difficult to state the differences between this 

 form and some of the near related species. The young are 

 more delicate and smoother than those of rozvclUi and at all 

 stages it is less inflated and more blunt behind than that 

 species. 



