﻿NEPHRONAIAS 



259 



mg, tawny, ravless : left valve with two heavy, torn pseudo- 

 cardinals, the posterior one more or less split into denticles 

 behind, and having- one strong- lateral; rig-ht valve with one 

 psendocardinal, a few denticles behind it and a low, wide lat- 

 eral ; beak cavities moderate ; muscle scars impressed, the an- 

 terior ones rough; nacre buff-colored. The pallial line has 

 faint radial pittings. 



Leng-th 60, height 43, diam. 27 mm. 



Isthmus of Darien. 

 {Jnio averyi Lea, Pr. Ac. N. Sci. Phila., III. 1859. p. 281 ; 11. 



Ac. N. Sci. Phila., IV, i860, p. 269, pi. xliv, fig. 149; Obs., 



VII, i860, p. 87. pi. XLIV, fig. 149. 

 Maro:aro?i (Unio) averyi Lea, Syn., 1870, p. 36. 

 Ncphronaias averyi Simpson, Syn.. 1900, p. 593. 



Both shells in the Lea collection, the only ones I have seen 

 belonging to the species, are probably males and have a straight 

 basal line. There is a faint secondary upper lateral in the left 

 valve. The shell is verv solid. 



Nkphronaias caldwellii (Lea). 



Shell irregularly elliptical, subinflated, scarcely subsolid, 

 with a feeble, double posterior ridge; beaks rather full and 

 high, turned forward over a small lunule, their sculpture fine, 

 irregular ridges slightly doubly looped and gradually passing 

 into that on the body of the shell ; surface concentrically sculp- 

 tured : epidermis olive-colored ; left valve with two ragged 

 pseudocardinals and two laterals, the upper feeble ; right valve 

 with one psendocardinal and a few denticles behind it, with 

 one lateral ; anterior scars rough ; nacre bluish, dull colored. 



Length 43. height 29, diam. 18 mm. 



Isthmus of Darien. 

 Unio caldivelUi Lea, Pr. Ac. N. Sci. Phila, II, 1858, p. 118; 



Jl. Ac. N. Sci. Phila., IV, i860, p. 265, pi. xliii, fig. 145; 



Obs., VII, i860, p. 83, pi. XLiii, fig. 145. — SowERBY, Conch. 



Icon., X\'L 1868, pi. Lxxxix, fig. 477. 

 Mar^iaron (Unio) caldwelUi Lea, Syn., 1870, p. 35. 

 Nephronaias caldwellii Simpson, Syn., 1900. p. S93- 



