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 CLEopoRA.—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 Cyrmputi1a.—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; 
txXvnt 335.6510, Id. 
Sect. I].—Gasteroropsa.— Organs of Progressive Mo- 
tion fitted 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, 
