186 Mr. W. H. Benson on Indian and Burmese 



of a wing, the short ligament, and the nature and position of the 

 teeth, all concur in warranting the separation of this shell from 

 U. marginalis, a small variety of which was sent to me from the 

 Berhampooter River by Major Rowlatt. 



I am indebted to Colonel Jenkins for the species here de- 

 scribed, as well as for the types of the Assamese forms U. invo- 

 lutus, U. Corbis, U. Radula, and U. Scobina, figured in Sylvanus 

 Hanley's Supplement to Wood's Index. U. Scobina was sub- 

 sequently published by Lea as U. fluctiger, without knowledge 

 of its habitat. 



2. Unio pachysoma, B., n. sp. 



U. testa transverse ovato-elongata, insequilaterali, tenuiuscula, valde 

 tumida, antice brevi rotundata, postice breviter alata, demum 

 modice acuminata, margine ventrali subrecto, postice ascendente ; 

 disco lseviusculo, polito, transverse striatulo, postice dense striato ; 

 epidermide viridi, fasciis nonnullis luteis radiisque obscuris ornata, 

 postice cserulescenti- viridi ; umbonibus prominentibus versus apices 

 contiguos minute radiato-costatis, carina umbonali prominente ob- 

 tusa, linea secunda radiata interjacente ; dentibus cardinalibus 

 duplicibus, laminatis, lateralibus modice elongatis, valvse sinistrse 

 solum duplicibus : margarita pallide purpurea, interdum salmonis 

 colore tincta. 



Long. 23, lat. 44, diam. 21 mill. 



Habitat in fluvio Berhampooter Assameusi. 



Anterior cicatrices distinct, posterior confluent, dorsal ones 

 under the cardinal teeth. The inner lamina of the latter in the 

 left valve sometimes obsolete. 



This is an inflated form of the caruleus type, quite devoid of 

 radiate rugse on the slopes, and with an excavated posterior 

 slope. The colour of the nacre is peculiar. I am indebted for 

 the type to Colonel Jenkins. 



A shell taken at Calcutta by Mr. W. Theobald, with a more 

 elongate-cylindrical form, an olive-green epidermis, and a salmon- 

 coloured nacre, and which I was at first disposed to consider to 

 be a variety of U. cceruleus, seems to be a distorted variety of 

 this species. A shallow shell, allied to the ordinary type of 

 U. cceruleus, was sent to me from Assam by Major Rowlatt in 

 abundance. 



3. Unio Theca, B., n. sp. 



U. testa transverse oblongo-ovata, valde insequilaterali, tenui, com- 

 pressa, antice et postice rotundata, superne subtusque convexius- 

 cula, margine ventrali medio recto ; disco subplanato, lseviusculo, 

 lineis transversalibus subrugosis versus margines notato ; epider- 

 mide pallide stramineo-lutea ; umbonibus planatis, decorticatis, 

 versus apices tenues prominulos concentrice sulcatis, postice lineis 

 duabus radiantibus tenuibus subelevatis munitis ; ligamento Ion- 



