144 MOLLUSCA. 



out the arctic seas. In swimming, it brings the tips of the 

 fins almost into contact, first on one side and then on the 

 other. 



GENUS CLEODORA. Body covered with a triangular py- 

 ramidal tunic. 



The fins are membranaceous. The mouth is situate be- 

 tween these, and is furnished with a semicircular lip. This 

 genus was instituted by Peron, for the reception of the Clio 

 of Brown. The C.pyramidata is the best ascertained spe- 

 cies. Brown's Jamaica, p. 386, tab. 43, f. 1. Two other 

 species were taken by the Congo expedition, in S. lat. 2. 14., 

 and E. long. 9- 55., and S. lat. 2.41., E.long. 9. 16., "both 

 having a spinous process on each side of their shell, near its 

 opening. One species is beautifully sulcated transversely, 

 and the other but slightly so." Tuckey's Narrative, p. 412. 



B. Fin single. 



GENUS CYMBULIA Tunic cartilaginous and trough- 

 shaped. 



The fin is single, divided into three lobes, one of which 

 is small, with two tubercles, and a minute fleshy beard. 

 This genus was instituted by Peron, in Annales du Museum, 

 t. xv. t. 3, f. 10, 11. 



SECT. II. GASTEROPODA. Organs of Progressive Mo- 

 tion fated for Creeping. 



This is one of the most extensive groups of molluscous 

 animals. The marks by which it is distinguished are well 

 defined, and the external and internal characters of the spe- 

 cies have been successfully illustrated. 



The Gasteropoda may be considered as having the body 

 protected dorsally by the cloak, and ventrally by the foot. 



