DESCRIPTION. 179 



Linnaean genus. Nor will the extension of the 

 membrane over the whole surface exclude it ; for 

 a regular gradation through the next species and 

 C. tunicatus may be traced from this to any indi- 

 viduals of the genus which are perfectly uncovered. 



The specimen figured in the plate and the 

 following one are both deposited in the British 

 Museum. They have been examined by Dr. 

 Blainville of Paris, by whom a communication 

 respecting them has, it is understood, been made 

 to the French Philomatique Society. The names 

 he has affixed to the two species are Cryptoconchus 

 porosus, and C. larvceformis. 



To the politeness of Dr. Leach, of the British 

 Museum, the author owes his opportunity of 

 making the annexed drawings and of inspecting 

 the mollusca. 



Fig. 2, 3, 4. C. larvajbrmis. 



Shell 8-valved, valves without any keel, dissi- 

 milar, covered partially with the membrane. 



Specimens having the three posterior valves 

 white and smooth, bluish flesh-coloured at the 

 sides, the others brown and striated ; coriaceous 

 membrane rough, cinereous olive, with a few 



