DESCUIPTION, 
179 
Linnsean genus. Nor will the extension of the 
membrane over the whole surface exclude it ; for 
a regular gradation through the next species and 
C. tunicaius 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 Phiiomatique Society. The names 
he has affixed to the two species are Cryptoconchiis 
porosus, and C. larvc^formis. 
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. larv(Ef or}nis. 
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 
