1866.] Contributions to Indian Malacology. 137 



thick form, with strong lateral teeth. The first shell is subalate pos- 

 teriorly, and the posterior margin is very bluntly biangulate, the 

 anterior margin is rounded at the end, but the slope thence to the 

 umbo is almost a right line ; the second shell is perfectly rounded both 

 before and behind. The shell of which the interior is figured corre- 

 sponds so ill with Miiller's description, being neither rhombic nor 

 thin, that it may certainly be neglected. The figure moreover is ill- 

 executed. 



Lamarck's description is a little different from Miiller's : " Unio testa 

 ovato-rJiombed, tenui, viridi, umbonibus rugosis, rug is undulato-flexuosis 

 sublongitudinalibus. Of the variety a he adds testa viridis, pubis 

 carina Icevigatd. His variety b is said to be the next species, U. 

 rugosus. 



The type shell in Mons. de la Serre's cabinet in Paris, which, by 

 the politeness of M. Chenu, the Curator, I was enabled to examine in 

 1862, is a thin broadly ovate form with small teeth, and a well 

 marked posterior wing. It measures 40 mm. from anterior to pos- 

 terior margin, and 33 from the umbo to the ventral margin, the latter 

 diameter being thus much greater in proportion to the former than 

 in Krister's type. The valves are inequilateral and much broader 

 behind than before, the anterior margin rounded, sloping away below 

 to the ventral side ; posterior margin bluntly biangulate, the two 

 angles rather wide apart. The form is common in Southern India 

 and Ceylon, and appears to have been generally accepted as the type. 



Both Lamarck's and Chemnitz's types are quite distinct from 

 Benson's U. favidens, which has been confounded with them. 



No. 2. — Unio rugosus, Gmelin. Rivers of Coromandel. 



Mya corrugata magna, Chemn. Conch. Cab. X. 346, PL 170, f. 1659. 



M. rugosa, Gmel. p. 3222, No. 32. 



Unio corrugata, [b.], Lam. VI., 78, No. 34. 



Unio rugosus, Kiister, Mart, and Chem. p. 290, PL 97, f. 5. 



Both this and the preceding species probably inhabit the Cauvery or 

 neighbouring streams. Kiister's figure represents an elliptical sub- 

 equilateral shell, with strong angulate sulcation at the umbones, 

 extending to within no great distance of the ventral margin. Gmelin's 

 original description is the following : — 



