NC.1205. SYNOPSIS OF THE NAIADES— SIMPSON. 607 



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

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

 XXX, fig. 27.— *B. H. Wright, Check List, 1888. 



* Margaron {Unio) neivcomManus Lea, Syn., 1860, p. 36. 



* Unio sagrinatus Sowerby, Conch. Icon., XVI, 1868, pi. lxvii, fig, 345. ' — 



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



Nicaragua; Venezuela? A specimeu 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., Xlt, 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. 



PMla., 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. 



* Unio gabhianus 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 unflgured and indeterminable. 



* Unio nuculinus Philippi, Zeits. filr Mai., V, 1848, p. 176, 



Nicaragua. Probably near cyrenoides. 



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



Nicaragua. This may equal encarpus Lea. 



DIGEN.^. 



Male shell inflated, truncated posteriorly; female shell compressed, 

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

 filled with a flap of the mantle. 



Genus TRITOGONIA Agassiz, 18B2. 



Tritogonia Agassiz, Arch, fiir Nat., 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 



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



