NO. 1205. SYNOPSIS OF THE NAIADES— SIMPSON. 859 



fTRAPEZOIDENS MISELLUS Morelet. 



"" Unio miselhis Morelet, Jl. cle Coiicli., XIII, 1865, p. 21 ; * Ser. Conch., IV, 1875, p. 

 341, pi. XIV, fig. 2.— *P^TEL, Conch. Sam., Ill, 1890, p. 159. 



* t Unio siamensis Lea, Pr. Ac. N. Sci. Phila., X, 1866, p. 133 ; " Jl. Ac. N. Sci. Phila., 



VI, 1868, p. 279, pi. XXXVIII, fig. 93 ; * Obs., XII, 1869, p. 39, pi. xxxviii, fig. 93. 



* Margaron (Unio) siamensis Lea, Syu., 1870, p. 57. 



TRAPEZOIDEUS PALLEGOIXI Sowerby. 



""Anodon pallegoixl Sowerby,^ Conch. Icon., XVII, 1867. pi. xvii, fig. 17. 

 "^Anodonta palUgoixi Clkssin, Conch. Cab. Ano., 1876, p. 210, pi. lxiv, fig. 6. — 

 ^P.ETEL, Conch. Sam., Ill, 1890, p. 183. 



Siam; Cambodia. 



TRAPEZOIDEUS PENINSULARIS Simpson. 

 ■ *Unio sumatrensis Sowerby," Conch. Icon., XVI, 1865, pi. xxviii, rig. 142. 

 Sumatra. 



TRAPEZOIDEUS EXOLESCENS Gould.^ 



*TJnio exolescens Gould, Pr. Bost. S. N. Hist., I, 1843, p. 141. — *Catlow and 

 Keeve, Conch. Nom., 1845, p. 59. — "H. and A. Adams, Gen. Eec. Moll., IF, 

 1857, p. 493.— *Haxley and Theobald, Conch. Ind., 1876, p. 43, pi. cvii, 

 fig. 5.— *P.etel, Conch. Sam., Ill, 1890, p. 152. 



*Margaron (Unio) exolescens Lea, Syn., 1852, p. 32; 1870, p. 51. 



Tavoy, Burma. 



TRAPEZOIDEUS THECA Benson. 



Tnio iheca Benson, Ann. and Mag., X, 1862, p. 186. — *Hanley and Theobald, 

 Conch. Ind., 1876, p. 6, pi. xii, fig. 5.— ^P.etel, Couch. Sam., Ill, 1890, p. 169. 



Cane Kiver, Bundelkliund, India. 



Genus ARCONAIA Conrad, 1865. 

 (Type, Triqueira lanceolata Lea.) 



* Arconaia Conrad, Am. Jl. Conch., 1, 1865, p. 234. 



Shell greatly elongated, inflated, solid, twisted on its axis, sometimes 

 straight, but generally having the posterior end curved strongly to the 

 right or left, with a decided posterior ridge on both sides of the shell, 

 ending in a blunt point, with usually a small ridge above on the j)Ost 

 slope; beaks rather low, sculpture not seen, but probably zigzag radial; 



' Sowerby says nothing abont teeth in his shell, which is from Siam. The teeth of 

 Lea's specimen of U. siamensis are scarcely developed, and a comparison of his ahell 

 with Sowerby's figure convinces me that they are very nearly allied. Lea's figure 

 shows the shell biangulate behind, which is an error. 



2 This is not Lea's smnairensis, nor that of Dunker. I have therefore changed the 

 name to peninsular is. I am not certain' as to its relations. It is not U. comptus 

 Deshayes and JuUien, as Fischer believes 



3 Gould did not figure this, and I have not seen the type. The shell figured as this 

 by Hanley and Theobald in the Conchologia probably belongs here. 



