858' PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



cscutclieou deep, triangular; beak cavities sliallow; anterior muscle 

 scars elongated; posterior faint; iridescent behind.^ 

 Animal unknown. 



LAMELLIDENS GUILLAINI Recluz. 



"" Arwdouta guillaini'RKCLVz, JI. de Conch., I, 1850, p. 55; "Zeits. fnrMal., VII, 1851, 

 p. 140.— ^Crosse, Jl. de Conch., XXXI, 1883, p. 222, pl.ix, fig. 4.— ■ P/etel, 

 Conch. Sam., Ill, 1890, p. 180. 



Biava, northeast Africa, in the Somali country. 



Genus TRAPEZOIDEUS Simpson. 

 (Type, Uniofoliacea Gould.) 



Shell trapezoid, much compressed, with a low posterior ridge, and 

 but slightly raised though pointed beaks, which seem to be sculptured 

 with irregularly radial ridges arranged in two imperfect chevron- shaped 

 loops; surface concentrically sculptured, often having irregular radial 

 ridges on the x)Osterior slope; epidermis yellowish-green or brownish, 

 with two or more green rays above the posterior ridge; teeth com- 

 pressed; two psendocardinals in the left valve, one under the beak, the 

 other in front, often not well separated, and two laterals; right valve 

 with two pseudocardinals and one lateral ; pseudocardinals all irregu- 

 lar, often pitted and peculiarly dentellate; laterals granular, showing 

 traces of vertical striation ; cavity of the beaks rather deep, compressed; 

 muscle scars shallow, anterior scars separate; nacre soft, creamy, yel- 

 lowish in the beak cavities. 



Animal unknown. 



tTRAPEZOIDEUS FOLIACEUS Gould. 



* Unio foliacea Gould, Pr. Post. Soc. N. Hist., I, 1843, p. 141 ; * Otia Conch., 1862, 



p. 191. 



* rw(o/o?iaceMsCATLOW and Reeve, Conch. Noni., 1845, p. 59. — *H.and A. Adams, 



Gen. Kec. Moll., II, 1857, p. 492.— *Hanley and Theobald, Conch. Ind., 1876, 

 p. 19, pi. XLii, fig. 3.—* Anderson, Yunnan Exp., 1877, p. 900, pi. lxxx, figs. 

 8-12.—* P.ETEL, Conch. Sam., Ill, 1890, p. 153. 



* Margaron ( Unio) foUaceus Lea, Syn., 1852, p. 39 ; 1870, p. 62. 



*tZ7ftia peguensis Anthony, Am. Jl. Conch., I, 1865, j). 351, pi. xxv, fig. 2. — 

 " SowKRBY, Conch. Icon., XVI, 1868, pi. xcv, fig. 519, — *P^tel, Conch. Sam., 

 Ill, 1890, p. 162. 



^Margaron ( Unio) peguensis Lea, Syn., 1870, p. 51. 



TRAPEZOIDEUS FOLIACEUS var. COMPTUS Deshayes and Jullien. 



* Unio comptua Deshayes and Jullien, Nouv. Arch, de Mus., X, 1874, p. 126, pi. vi, 



figs. 3, 4. 



* Unio fragiles Nevill, Jl. As. Soc. Peng., XLVI, 1877, p. 39. — *Anderson, Yunnan 



Exp., 1877, p. 400, pi. lxxx, figs. 8-12. 



Burma; Cambodia. 



' I hardly know where to place this, as the descrix^tion is lacking in several essen- 

 tial characters. It is probable that the beak sculpture is much like that of Lamelli- 

 dens instead of being properly concentric, and it maybe a subgenus of that group. 



