148 COKBULID.E. 



A. PR.ETENUIS, Pulteney et nobis. 



Cochleodesma, Couthouy. 



C. pratenue, Brit. Moll. i. p. 235, pi. 15. f. 4. 



As the animal of this species varies in no material cha- 

 racter from our type, we refer to our account of it in the 



1 British Mollusca/ which volumes we suppose to be in the 

 hands of every cultivator of this branch of natural history. 

 The specialties of the shell are not of moment in a generic 

 point of view. The ossicle is large, and more apparent than 

 usual. 



A. DISTORTA, Montagu et nobis. 



Thracia distorta, Brit. Moll. i. p. 231, pi. 17. f. 1, 2, 3, 8 ; (animal) 

 pi. H. f. 5. 



For an account of this animal, we refer to notes of ours in 

 the ' British Mollusca/ 



The ossicle is the most minute of the tribe. 



A. CONVEXA, Wood et nobis. 

 Thracia convexa, Brit. Moll. i. p. 229, pi. 16. f. 1,4. 



We have not seen the animal of this species, but cannot 

 doubt that it marches with its congeners. We have shells in 

 our collection containing the usual arcuated ossicle. Small 

 shells are frequently met with at Exmouth, but those of 



2 inches transverse measure are very rare. 



CORBTTLIDJ3. 



This little group consists of three genera, Corbula, Sph&nia, 

 and Pandora ; the first has only one established species ; 

 Sphcenia, one ; and the last, two ; one of which is probably not 

 indigenous. The Corbulida, by the closed mantle and short 

 united siphons, are allied to the Anatinidae and Saxicavce. 



