266 PLEUROBRANCHIDZ. 
prevent disputes about their respective oyster hmits, having 
debarred their entry into the Exe. I am very desirous to 
review these species; naturalists visiting the French coasts 
ought to be on the look-out, as the oyster dredgers, if pro- 
perly instructed, can furnish both these animals as well as the 
Chitons. 
CALYPTRAA, Lamarck. 
C. stvensis, Linnzus et Auct. 
C. sinensis, Brit. Moll. ii. p. 463, pl. 60. f. 3, 4,5; (animal) pl. B. B. 
f. 8-13. 
I can say nothing of this species beyond the general remarks 
already made: I have never seen the animal in a sufficiently 
lively condition to exsert the organs. In the hope of examining 
these animals under more favourable circumstances, I refer in 
the interim to the ‘ British Mollusca,’ vol. 11. p. 463, for some 
account of the C. sinensis. 
PLEUROBRANCHIDA. 
The above family, with the Aplysiade and Bullide, cousti- 
tute a group of the congressional hermaphrodital division. 
We designate the first family Pleurobranchiata, from the 
branchiz being fixed between the disks on one side only ; and 
the Aplysiade and Bullide, Cryptibranchiata, from their 
branchial mechanism being deposited in variously-situated 
dorsal crypts, which differ in character and position from 
those of the cervical regions. The heart in this group is 
placed laterally, or somewhat anterior to the branchiz, in- 
stead of posterior, as in the major part of the Gasteropoda. 
M. Cuvier’s admirable memoirs and figures ilustrate both 
positions. 
The Pleurobranchide are the Semiphyllidiens of Lamarck, 
and contain two genera, only one being British, with two 
species; it cannot, on account of material anatomical consi- 
derations, be associated with the Chitones and Patelle ; only one 
