Species of the Genus Unio. 189 



3. var. Delta. Epidermis olive-green and yellow, rayed; nacre 



salmon-coloured ; rugae on umbones very distinct, some also 

 on the upper part of the umbonal hinder slope; lunule 

 somewhat broader than in the type ; cardinal teeth narrower. 

 Long. 34, lat. 47, diam. 24 mill. 



I took a single specimen in the River Jellinghy, in 1831, in 

 the upper part of the Gangetic Delta, Bengal. 



4. var. Chrysis. Longer and less broad in proportion ; epidermis 



a beautiful green, banded more or less with yellow ; umbonal 

 rugse very strong and extended ; cardinal teeth mostly nar- 

 rower than in the type ; nacre salmon-tinted. 

 Long. 27, lat. 35, diam. 16 mill. 



River Dojora at Kareily Ghat, near Bareilly. Single valves 

 are long. 33, lat. 43 mill. 



5. \ar. vmdula. Form of type, but more compressed; colour 



as in the last; cardinal teeth broad; nacre bluish white; 



umbonal rugse as in 4. 

 Long. 27) lat. 40, diam. 17 mill. 



Standing water, or " jheel,'^ between Humeerpore and Someer- 

 pore, Bundelkhund. 



6. var. densa. More solid and tumid ; epidermis yellow-brown, 



eroded ; lunule as in type ; shell more oblique. 

 Long. 33, lat. 47, diam. 24 mill. 



Ganges River, above Chunar, between Allahabad and Benares. 



Great confusion appears to exist with reference to the true 

 Unio corrugatus. Lamarck describes it, including U. rugosa, 

 Gm., as " ovato-rhombea, tenui,^' and the full-grown shell as 

 " rounded rhomboid.'^ Lea, in the third edition of his Synopsis, 

 includes U. corrugatUy rugosa, and spuria, Lk., as synonyms, and 

 nodosa, with a mark of doubt. He also adds the solid U. 

 favidens, Bens., with the very distinct and thick Tenasserim 

 species U. Tavoyensis, Gould; but in vol. vii., in his remarks on 

 U. Nagporensis, he alludes to U. favidens as a distinct species. 

 A form allied to my var. Delta was supposed by Mr. Hanley to 

 be the real type ; and a Ceylon shell is also referred to it in 

 Sir E. Tennent's List. 



The winged young of U. favidens, 17 mill, in breadth, is thin 

 and ovate-rhomboid ; and the very young shell, which is more 

 transverse, is angularly corrugate over the whole surface. The 

 former approaches the figure of Mija spuria as copied by Wood. 



A thin, compressed, rhomboid-ovate Unio, with radiate-sulcate 

 beaks, found by Dr. Day on the Malabar coast, comes near La- 

 marck's description of his var. rugosa. It may possibly be the 



