TRAPEZOIDEUS. 195 



320. Trapezoideus exolescens (Go^ihf). 



Trappzoideidi cvoIcaccu^ ((Joiild); Sinipsou, Washington, D.C, 

 Smitlis. Inst., Nut. Mus. Proc. xxii, 1900, p. 8r)9. 



Unio exolescens, Gould, Proc. Boston, Soc. Nat. Hist, i, 1843, 

 p. 141 ; Catlow it IJeeve, Conch. Nom. 1845, p. 59 ; II. (fc 

 A. Adams, Gen. Ilec. Moll, ii, 1857, p. 493: II. & T., C. I. 

 1876, p. 43, pi. 107, fi^-. 5 ; Picte^, Conch. Saiu. iii, 1890, 

 p. 152. 



Marfjavon {Unio) exolescens, Lea, Syn. 1852, p. 32; 1870, p. 51. 



Original description : — Testa Iransverso-oblonj^ata, inequikiterali, 

 subconipressa, fusco-viresceiite ; postice dilatata, sub-biangulata ; 

 umbouibus subelevatis : deutibus cardinalibus parvis, obliquis, 

 interdura exoletis ; lateralibus reinotis, reotis ; niargarita livida 

 vel ferruginea. 



Long. 32, lat. 70, diam. 15 mm. 



Ilab. Tavoy ; also Bbamo (Indian Museum Collection). 



321. Trapezoideus theca (Benson). 



Trtipezoideus theca (IJensou) ; Simpson, Washington, D.C, Smiths. 



Inst.. Nat. Mus. Proc. xxii, 1900, p. 859. 

 TJnio theca, Benson, A. M. N. II. x, 1862, p. 186 ; IL & T., 



C. I. 1876. p. 6, pi. 12, %. 5; Pfetel, Conch. Sam. iii, 1890, 



p. 169. 



Original description : — Testa transverse oblongo-ovata, valde 

 iiiaequilaterali, tenui, compressa, antice et postice rotundata, 

 superue subtusque convexiuscula, margiue ventrali medio recto; 

 disco subplanato, laeviusculo, liueis traiisversalibus subrugosis 

 versus margines notato ; epidermide pallide stramineo-lutea ; 

 umbonibus plaaatis, decorticatis, versus apices tenues prominulos, 

 concentrice sulcatis, postice lineis duabus radiantibus tenuibus 

 subelevatis muuitis; ligamento lougiore ; dentibus cardinalibus 

 laminatis, tenuibus, brevibus, utriusque valvse duplicibus, valvje 

 dextrte prope marginem aiiteriorem sitis, obliquis ; sinistrse lobo 

 subapicaii transverse, anteriore obliquo, lateralibus elougatis, vix 

 curvatis, valva? dextrte simplicibus, sinistrae duplicibus ; margarita 

 lutea, versus marginem ventralem albida. 

 Long. 20, lat. 40, diam. 10 mm. 

 Hab. Kiver Cane, near Banda, Bundelkhund. 

 The above description is amplitied by tbe following notes: — 

 " Interior of sliell transversely siibplicate ; cavity of beaks 

 shallow. Anterior cicatrices separate, posterior confluent, apical 

 ones in the cavity of the beaks. Some slight rugse are visible on 

 the posterior slope at right angles to the stria? of growth. 



" The shell is somewhat wider posteriorly than 



anteriorly. The pale opaque straM-colour of the unpolished 

 epidermis is also a peculiar feature, not observable in any other 

 JS'ortliern Indian species. 



tbe double umbonal line, apparent occasionally in adult 



specimens of r. [{L.) L.] marginulis, is conspicuous." 



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