188 j\Ir. W. 11. Benson on Indian and Burmese 



the locality indicated. Although belonging to the favidens type 

 with reference to its teeth, it approaches that of cceruleus in 

 other respects. A delicate specimen which I got in the Gungun 

 River, near Moradabad, appears to be a younger variety. Its next 

 nearest Indian relation is a similarly radiate-sulcate compressed 

 shell, taken by Dr. Bacon in Purneah and the Mahanuddy River, 

 far to the eastward ; but that form is narrower, has a shorter 

 wing, is truncate posteriorly, and has the cardinal teeth (when 

 not obsolete) more oblique, and the lateral teeth curved, ap- 

 proaching the Borneo species Unio plicatulus, Lea. 



5. Unio favidens, B. 



U, testa transverse ovata, insequilaterali, crassa, subtumida, autice 

 rotundata, postice subalata, declivi, angulata, demum obtusa, mar- 

 gine ventrali convexiusculo ; disco inaequaliter sulcato ; epidermide 

 olivaceo-fusca, versus marginem ventralem luteo-olivacea, postice 

 viridi parce fasciata ; umbonibus tumidis, prominentibus, decorti- 

 catis, sulcis radiatis angulato-flexuosis indutis ; lunula impressa, 

 elliptica, decorticata ; ligamento elongato ; carina umbonali laevi- 

 uscula, linea unica vix elevata notata ; dentibus cardinalibus 

 crassis, fortiter radiato-rugosis, lateralibus obliquis, elongatiusculis, 

 valvee dextrse duplicibus, sinistrse subtriplicibus : margarita pallida 

 lutea, iridescente. 



Long. 45, lat. 66, diam. 30 mill. 



Habitat in fluvio Gange superiore. 



The anterior and posterior cicatrices are distinct, the apical 

 ones disposed on the under side of the cardinal tooth. 



This fine shell, the type of the species, was taken by me in 

 the Ganges at Bhitoura, between Cawnpore and Allahabad, in 

 1824, and the outline of it was figured in plate 7. fig. 1 of the 

 1st volume of 'Gleanings in Science' for 1829, from a private 

 lithographic copy made in 1826, by Mr. Wood, from my rough 

 sketch. The Bhitoura specimens were the largest which I cap- 

 tured during many years' residence in the country. 



The following are the chief varieties of U. favidens. Some of 

 them may possibly be regarded as separate species. 



1. var. marcens. Banded with olive and green; nacre salmon- 



coloured; beaks nearly smooth, eroded; sulci obsolete, 



lunule narrow. 

 Long. 44, lat. 66, diam. 27 mill. 

 From the Berhampooter River, Assam. Colonel Jenkins. 



2. var. trigona. Shell with a piceous epidermis, more oblique ; 



beaks and nacre as in type ; lunule broad. It shows an in- 

 clination to verge towards U. triembolus. 



Long. 44, lat. Q7, diam. 27 mill. 



From Nujeebabad, in the north-west of Rohilkhund. 



