2C6 PLEUEOBRANCHID^. 



prevent disputes about their respective oyster limits, 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. 



CALYPTR^EA, Lamarck. 



C. SINENSIS, Linnseus et Auct. 



C. sinensis, Brit. Moll. ii. p. 463, pi. 60. f. 3,4,5; (animal) pi. 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. ii. p. 463, for some 

 account of the C. sinensis. 



PLEUROBRANCHID^. 



The above family, with the Aplysiadce and Bullidce, consti- 

 tute a group of the congressional hermaphrodital division. 

 We designate the first family Pleurobranchiata, from the 

 branchiae being fixed between the disks on one side only ; and 

 the Aplysiadce and Bullidce, 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 branchiae, in- 

 stead of posterior, as in the major part of the Gasteropoda. 

 M. Cuvier's admirable memoirs and figures illustrate both 

 positions. 



The Pleurobranchidfe 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 iheChitones and PateUfC only one 



