194 Mr. W.H.Benson on Indian and Burmese Species o/Unio. 



dente cardinali (valvse dextrse) brevi, crassa, prominente, radiato- 

 sulcata, laterali elongata, subduplicata, intus crenulata : margarita 

 albida, iridescente. 



Long. 21, lat. 42, diam. 16 mill. 



Habitat in regione Ava. 



The anterior cicatrices are distinct, the larger deeply excavated 

 under the cardinal tooth, the smaller punctiform, posterior ones 

 confluent. Cavity of the beaks very shallow. Dorsal cicatrix 

 under the cardinal tooth. The cardinal ligament is lengthened. 

 The single right valve sent for examination by Mr. Theobald is 

 decorticate and worn. 



The Chinese lengthened lanceolate Unio Grayanus, Lea, and 

 the Siamese U Sagittarius, Lea, are allies of this shell in regard 

 to form ; but the thick prominent cardinal tooth, and the ex- 

 ceedingly short anterior portion of the shell suddenly deflected 

 from the beak, are sufficient characters for the recognition of the 

 species, independently of other differences. It is also more 

 narrow at the posterior end than U. Sagittarius. The angle of 

 the umbonal slope, with the area intermediate between the slope 

 and the hinge, and descending to the latter, are also peculiar 

 features. 



The only allied species which exhibits a similarly short ante- 

 rior portion of the shell is U. truncatus, Swains., in which, how- 

 ever, it forms an intermediate sinus, instead of descending sud- 

 denly and directly as in U. Pugio. There is also something in 

 the general form connecting the two shells; but Swainson's 

 species is tumid, not flattened, has a more prominent umbo, and 

 is not so narrow posteriorly, while the peculiar angle and cardinal 

 descent of the umbonal slope afford additional characters for 

 separating U. Pugio from the rare shell, of unknown locality, in 

 Mrs. Mawe's cabinet. 



The habitat of Unio Nuttallianus, Lea, is merely announced 

 as Indian by the author. I received specimens from Major 

 Rowlatt from Assam, where, with the thin, tumid, and peculiarly 

 formed U. invohitus, nobis, it represents the thin and compressed 

 Gangetic species, U. olivarius, Lea, some specimens of which, from 

 the rivers Jumna and Dojora, approach it in the more angular 

 form of the posterior end. The epidermis varies from a fine 

 green to olive, and the salmon-colour of the nacre is occasionally 

 very rich. The beaks exhibit slight nodules in rayed lines ; and 

 coloured rays are also visible on the epidermis. It attains the 

 following dimensions: — long. 25, lat. 40, diam. 18 mill. 



My largest specimens of a variety of Unio olivarius, Lea, 

 taken in the River Ramgunga, above Moradabad, are 50 mill, 

 in breadth by 28 in length, and 16 in diameter. It is widely 

 distributed in the Gangetic region, and is most abundant in the 



