Nc.1205. SYNOPSIS OF THE NAIADES SIMPSON. 607 



*t Unio newcombianus LEA, Pr. Ac. N. Sci. Phila., VIII, 1856, p. 103; * Obs., VI, 

 1857, p. 32, pi. xxx, fig. 27; *J1. Ac. N. Sci. Phila., Ill, 1858, p. 312, pi. 

 xxx, fig. 27. *B. H. WRIGHT, Check List, 1888. 



* Margaron ( Unio) newcombianus LEA, Syii., 1860, p. 36. 



* Unio sagrinatus SOWERBY, Conch. Icon., XVI, 1868, pi. LXVII, fig. 345. ' 



P^TKL, Conch. Sam., Ill, 1890, p. 166. 



Nicaragua; Venezuela 1 ? A specimen in the U. S. National Museum 

 from the Morelet collection is marked with the latter locality. 



tPLAGIOLA ENCARPA Lea. 



* Unio encarpus LEA. Pr. Ac. N. Sci. Phila., XII, 1868, p. 95; * Jl. Ac. N. Sci. 



Phila., VI, 1868, p. 294, pi. XLII, fig. 105; * Obs., XII, 1869, p. 54, pi. XLII, 

 fig. 105.* B. H. WRIGHT, Check List/ 1888. 

 Margaron ( Unio) encarpus LEA, Syn., 1870, p. 35. 



Nicaragua. 



(Group of Plagiola nicaraguensis.} 



Shell much like that of cyrenoides, but simply covered with coarse, 

 irregular, concentric ridges, and having no radiating grooves or wrin- 

 kles, faintly rayed in umbonal region. Animal as in Cyrenoides group. 



t PLAGIOLA NICARAGUENSIS Lea. 



* Unio nicaraguensis LEA, Pr. Ac. N. Sci. Phila., XII, 1868, p. 95; * Jl. Ac. N. Sci. 



Phila., VI, 1868, p. 296, pi. XLIII, fig. 107; *Obs.," XII, 1869, p. 56, pi. XLIII, 

 fig. 107.* B. H. WRIGHT, Check List, 1888. 



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



* I'nio gabbianus LEA, Pr. Ac., N. Sci. Phila., XII, 1868, p. 95; *J1. Ac., N. Sci. 



Phila., VI, 1868, p. 295, pi. XLIII, fig. 106 ; * Obs., XII, 1869, p. 55, pi. XLIII, fig. 

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



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



Nicaragua. 



The following species are untigured and indeterminable. 



* Unio nuculinus PHILIPPI, Zeits. fur Mai., V, 1848, p. 176. 

 Nicaragua. Probably near cyrenoides. 



* Unio (Plagiola?) imbricatus M()RCH, Mai. Bl., VII, 1861, p. 205. 



Nicaragua. This may equal encarpus Lea. 



DIGEN^E. 



Male shell inflated, truncated posteriorly ; female shell compressed, 

 expanded into a broad wing behind the post ridge, the wing being 

 tilled with a flap of the mantle. 



Genus TRITOGONIA Agassiz, 18S2. 

 Tritogonia AGASSIZ, Arch, fiir ]S T at., 1852, p. 48. 



Shell solid, elongate rhomboid, having a strong, irregular posterior 

 ridge, obliquely truncated behind in the male, in the female this region 

 is somewhat compressed and rounded; base incurved; whole surface 



1 Changed in errata by the author to U. newcombianus. 



