NO. 1205. SYNOPSIS OF THE NAIADES SIMPSON. 593 



1888.* P.ETEL, Conch. Sam., Ill, 1890, p. 166.* FISCHER and CROSSE, Misa. 

 Sci., Pt. 7, II, 1894, p. 601, pi. LXVII, figs. 2, 2a. 



* Margaron ( Unio) sapotalensis LEA,t Syn., 1852, p. 29; 1870, p. 45. 



Sapotal River, Vera Cruz, Mexico. 



(Group of Nephronaias averyi.) 1 



Shell triangular-ovate, bluntly pointed in front, and biangulate 

 behind, considerably inflated, irregularly silicate; umbonal region mod- 

 erately developed ; beaks sculptured with fine, irregular ridges which 

 have a tendency to fall into two rounded loops; pseudocardinals 

 slightly compressed, ragged; laterals having feeble, oblique striation; 

 front part of the shell somewhat thickened; posterior part thinner; 

 nacre dull, whitish. 



Animal unknown. 



t NEPHRONAIAS AVERYI Lea. 



* Unio averyi LEA, Pr. Ac. N. Sci. Phila., Ill, 1859, p. 281; * Jl. Ac. N. Sci. Phila., 



IV, 1860, p. 269, pi. XLIV, fig. 149 ; * Obs., VII, 1860, p. 87, pi. XLIV, fig. 149. 



* B. H. WRIGHT, Check List, 1888. 



* Margaron ( Unio) averyi LEA, Syn., 1870. p. 36. 



Isthmus of Darien. 



f NEPHRONAIAS CALDWELLII Lea. 



* Unio caldwellii LEA, Pr. Ac. N. Sci. Phila., II, 1858, p. 118 ; * Jl. Ac. N. Sci. Phila., 



IV, 1860, p. 265, pi. XLIII, fig. 145; * Obs., VII, i860, p. 83, pi. XLIII, fig. 145. 

 *SOWERBY, Conch. Icon., XVI, 1868, pi. LXXXIX, fig. 477. *B. H. WRIGHT, 

 Check List, 1888. * P.ETEL, Conch. Sam., Ill, 1890, p. 147. 



* Margaron ( Unio) caldwellii LEA, Syn., 1870, p. 35. 



Isthmus of Darien. 



(Group of Nephronaias macnielii.) 



Shell solid, slightly sulcate, biaugulate behind, covered with a dull, 

 olivaceous epidermis and having faint, bluish green rays ; beaks rather 

 full, sculpture feeble, consisting of slightly outlined ridges, somewhat 

 doubly looped, the looped lines becoming swollen or nodulous at their 

 bases; pseudocardinals compressed and ragged; laterals obliquely 

 striated; nacre bluish white, very soft and brilliant, somewhat irides- 

 cent posteriorly; male and female shells differing but slightly. Animal 

 unknown. 



fNEPHRONAIAS MACNIELII Lea. 



* Unio macnielii LEA, Pr. Ac. N. Sci. Phila., XIII, 1869, p. 124; * Jl. Ac. Nat. Sci. 



Phila., 1874, p. 25, pi. vin, fig. 22; * Obs., XIII, 1874, p. 29, pi. vin, fig. 22. 



* B. H. WRIGHT, Check List, 1888." P.ETEL, Couch. Sam., Ill, 1890, p. 158. 



Nicaragua. 



1 1 have only seen two specimens of Lea's Unio averyi and one of his U. caldwellii, 

 and I can not be certain as to their systematic position. In the latter the beak 

 sculpture, which is slightly worn, is much of the character of the species of Neph- 

 ronaias generally, and not like that of Unio, and though somewhat worn the shell 

 shows traces on the posterior end of faint, bluish green rays. One of the former is 

 slightly more inflated in the post- basal region than the other. 

 Proc. N. M. vol. xxii 38 



