1866.] Contributions to Indian Malacology. 139 



Lam. It differs totally from all tlie shells referred to that species, 

 and all its numerous varieties are easily distinguished both from 

 Lamarck's and Chemnitz's types of corrugatus. U. favidens is more 

 inequilateral, it is a thicker shell with much stronger and broader 

 cardinal teeth. The type, too, is more angulate, both anteriorly and 

 posteriorly. The following varieties of U. favidens, with their 

 localities, are described by Mr. Benson in the Ann. and Mag. Nat. 

 Hist. Vol. X, pp. 188, 189. 



Unio favidens, type. Bhitoura on the Ganges between Cawnpore 

 and Allahabad. 



1 var. marcens, Burhampooter river, Assam. 



2 ,, trigona, Nujeebabad in the north-west of Rohilkund. 



3 ,, Deltce, Jellinghy river, Bengal. 



4 ,, Chrysis, Dojora river, Kareily G-hat near Bareilly. 



5 ,, viridula, " Jheel" between Humeerpore and Someer- 



pore, Bundelkund. 



6 ,, densa, Ganges river above Chunar. 



No. g. — Unio Ceruleus, Lea. — Hoogly river, 100 miles above 

 Calcutta. 



Lea, Trans. Am. Phil. Soc. IV, 95, PI. 13, f. 25. 



Benson, J. A. S. B. IV. 450. 



Kiister, Mart, and Chem. p. 228, PI. 77, fig. 4. 



The two figures agree perfectly. The type is a very thin shell, 

 with fine lamellar teeth. Specimens exist in the Asiatic Society's 

 Museum, brought from Bhagulpoor. The form is widely distributed 

 in N. India ; I have even a variety from Sind. 



No. 7. — Unio bilineatus, Lea. Hoogly river with the last. 



Symphonota bilineata, Lea, Trans. Am. Phil. Soc., IV. 98, pi. 11, f. 19. 

 Benson, J. A. S. B. IV. 452. 



Benson, (Ann. Mag. Nat. Hist. Ser. 3, Vol. X., pp. 187, 195) shews 

 that this is merely the very young form of U. marginalis, Lam. He 

 is unquestionably correct. The " two delicate lines passing from the 

 beaks to the posterior region" are, like many other umbonal mark- 

 ings, characteristic of young shells, and disappear gradually with age. 

 The remains of them, much blunted, are often to be detected on 

 adults. 



