﻿NF.PIIRONAIAS 263 



two very ragged, somewhat irregular, subconipressed pseudo- 

 cardinals and two curved laterals ; right valve with one pseudo- 

 cardinal and a faint tooth above it, with one lateral ; beak cav- 

 ities rather deep ; muscle scars impressed ; nacre bluish-white. 



Female shell full at the posterior base and rather blunt be- 

 hind : that of the male scarcely, if at all, inflated at the poste- 

 rior base. 



Length 75, height 47, diam. 32 mm. 



Nicaragua ; Guatemala ; Chagres River, Colombia. 

 Unio roivellii Lea, Pr. Ac. N. Sci. Phila., IH, 1859, p. 153; Jl- 



Ac. N. Sci. Phila., IV, i860, p. 256, pi. xl, fig. 136; Obs., 



VII, p. 74, pi. XL, fig. 136.— SowKRBY, Conch. Icon., XVI, 



1868, pi. Lxxxviii, fig. 471- 

 Margaron (Unio) rowellii Lra, Syn., 1870, p. 35. 

 Ncphronaias rozvellii vSimpson, Syn., 1900, p. 594. 



Rather more inflated and pointed behind than N. macnielii, 

 somewhat more inflated and darker colored than U. goascor- 

 ancnsis, darker and less rayed than A^. oregonensis. These 

 four species are very difficult to separate and Dr. Lea had all 

 four of them in his collection labeled Unio rozvcllii. 



Nephronaias HjALMARSONi (Dunker). 



Shell small, irregularly long elliptical, moderately com- 

 pressed, narrowed and rounded in front, rather wider and 

 subtruncate above at the posterior end ; posterior ridge strong, 

 scarcely double, ending in a blunt point near the base line of 

 the shell ; beaks but little elevated, about one-third of the way 

 back from the anterior end ; base rounded ; surface covered 

 with strong, concentric, sometimes anastomosing plaits ; epi- 

 dermis dirty yellow ; pseudocardinals someWbat thick, oblique, 

 deeply furrowed but not crenulated ; nacre bluish-white. 



Length 36, height 18.5, diam. 11 mm. 



Rio Chamelicon, Honduras, near Guatemala. 

 IJnio hjalmarsoni DuNKEiii, Mai. Blatt, V, 1858, p. 227. — von 



Martens, Biol. Cent. Am., Moll., 1900, p. 509, pi. xxxvin, 



figs, ir, iia. 



