MOLLUSC A. 143 



cur on the caudal extremity of the body, as the branchiae, 

 and even describes the pulmonary vein which conveys the 

 blood from these to the heart. But, in his Regne Animal, 

 he states it as the opinion of M. Blainville, that the fin-like 

 expansions of the neck contain the branchiae on their sur- 

 face, as in the case of Clio. The rectum and oviduct ter- 

 minate under the right wing. Cuvier has figured and de- 

 scribed the only known species, which he terms Pneumo- 

 dermon Peronii, the trivial name being in honour of the 

 discoverer, M. Peron. 



Posterior extremity simple. 



GENUS CLIO Body ovate, with the tunic elongated and 

 membranaceous. 



The head is divided into two lobes, the summits of which 

 are furnished with tentacula. The existence of eyes has 

 not been ascertained. The mouth is transverse, with two 

 lateral longitudinal lips. On each side of the neck arise two 

 blunt, conical, fin-like expansions, with a fine reticulated 

 surface, considered as serving the double purpose of fins 

 and branchiae. The anus and orifice of generation termi- 

 nate under the base of the right branchia. The viscera do 

 not fill entirely the cavity of the inner bag. The gut makes 

 only one fold. 



The genus Clio was originally instituted by Brown in 

 his Natural History of Jamaica. It was afterwards em- 

 braced and modified by Linnaeus and Pallas, in such a man- 

 ner as ultimately to exclude the species for the reception of 

 which Brown originally formed it. It contains two species, 

 the most remarkable of which is the Clio borealis. Mr. 

 Scoresby, in his valuable work on the Arctic Regions, states, 

 (vol. i. p. 544), that it occurs in vast numbers in some situ- 

 ations near Spitzbergen, but is not found generally through- 



