TKAPEZOIDEUS. 195 



320. Trapezoideus exolescens (Gould). 



Trapezoideus exolescens (Gould) ; Simpson, Washington, D.C., 

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



Unto evolescens, Gould, Proc. Boston, Soc. Nat. Hist, i, 1843, 

 p. 141 ; Catlow & lleeve, Conch. Nona. 1845, p. 59 ; H. & 

 A. Adams. Gen. Eec. Moll, ii, 1857, p. 493: H. & T v C. I. 

 1876, p. 43, pi. 107, fig. 5 ; Psete), Conch. Sam. iii, 1890J 

 p. 152. 



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



Original description: Testa transverso-oblongata, inequilaterali, 

 subcompressa, fusco-virescente ; postice dilatata, sub-biangulata ; 

 umbonibus subelevatis; dentibus cardinalibus parvis, obliquis, 

 interdum exoletis; lateralibus reraotis, rectis ; margarita livida 

 v'el ferruginea. 



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



Hob. Tavoy ; also Bhamo (Indian Museum Collection). 



321. Trapezoideus theca (Benson}. 



Trapezoideus theca (Benson) ; Simpson, Washington, D.C., Smiths. 



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

 Unio theca, Benson, A. M. N. H. x, 1862, p. 186; II. & T., 



C. I. 1876, p. 6, pi. 12, fig. 5 ; Psetel, Conch. Sam. iii. 1890, 



p. 169. 



Original description : Testa transverse oblongo-ovata, valde 

 inaequilaterali, tenui, compressa, antice et postice rotuhdata, 

 superne subtusque convexiuscula, margine ventrali medio recto; 

 disco subplanato, Iseviusculo, lineis trarisversalibus subrugosis 

 versus margines notato ; epidermide pallide stramineo-lutea ; 

 umbonibus planatis, decorticatis, versus apices tenues prominulos, 

 concentrice sulcatis, postiee lineis duabus radiantibus tenuibus 

 subelevatis munitis; ligamento longiore ; dentibus cardinalibus 

 laminatis, teuuibus, brevibus, utriusque valvae duplicibus, valvae 

 dextras prope marginem anteriorem sitis, obliquis ; sinistrse lobo 

 subapicali transverse, anteriore obliquo, lateralibus elongatis, vix 

 curvatis, valvae dextrse simplicibus, sinistrse duplicibus ; margarita 

 lutea, versus marginem ventralein albida. 

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

 Hob. River Cane, near Ban da, Bundelkhund. 

 The above description is amplified by the following notes : 

 " Interior of shell transversely subplicate ; 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 striae of growth. 



" The shell is somewhat wider posteriorly than 



anteriorly. The pale opaque straw-colour of the unpolished 

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

 Northern Indian species. 



the double umbonal line, apparent occasionally in adult 



specimens of U. [(L.) L.~] marginalis, is conspicuous." 



o2 



