CO VERED-GILLED S UBGRO UP 



3337 



Clione, 

 (Somewhat enlarged.) 



short spire, and the aperture somewhat prolonged at the base. The lip of the aper- 

 ture is simple, but the columella is reflexed. The fins of L. helicina are broad and 

 squarish at the ends and notched on the inner edge. The 

 operculum is oblong, transparent, paucispiral, the nucleus be- 

 ing lateral. This mollusk lives in immense shoals in the 

 Greenland seas, and it is one of those fed upon by various 

 whalebone whales. Two species only are known of Peraclis. 

 The shells are excessively fragile, sinistral, rather like a fresh- 

 water Physa in shape, but having the aperture produced below 

 into an acute rostrum. The animal has a minute glassy 

 operculum, and differs from Limacina in having a distinct 

 head, prolonged into a proboscis, and other anatomical char- 

 acteristics. Both forms occur in the Atlantic, but P. reticulata 

 is also known from the Pacific and the Mediterranean. 



The mollusks of the family Cavoliniidce have external 

 semitransparent shells, which are nonoperculate, bilaterally 

 symmetrical, and not spirally coiled. They are variable in form in the different 

 genera. The animals are completely retractile within the shell, and the form of 



the fins and of the hinder lobe of the foot 

 varies considerably. The mouth, lips, and 

 tentacles are the same as in Limacina. Three 

 genera are comprised in this family, namely, 

 Clio, Cuvierina, and Cavolinia. Clio is subdi- 

 vided by Dr. Pelseneer into four groups, 

 Creseis, Hyalocylix, Styliola, and Clio. In 

 Creseis the shell is elongated, conical, circular 

 in section, smooth, and the embryonic portion 

 marked off by a deep constriction. The 

 shell of Hyalocylix is elongate, conical, oval 

 in section, with a recurved apex, and marked 

 with transverse grooves and ridges. H. 

 striata, the only known species of this genus, 

 is cosmopolitan. Styliola has a slender taper- 

 ing shell, sometimes an inch in length, and 



not more than a sixteenth of an inch in diameter at the aperture. It appears quite 

 smooth and glossy, and, like Hyalocylix, occurs in all tropical seas. Clio is one of 

 the most beautiful of all Pteropods. The shell is often rather 

 triangular in shape, keeled along the sides, the lateral angles being 

 sometimes produced into long, straight, sharp spines. It is of a 

 most delicate glassy substance, and highly glossy. The so-called 

 genus Balantium is synonymous with this group. Eight species 

 are recognizable. The genus commonly known as Cuvieria con- 

 tains only a single species (C. columnella}, which has been obtained 

 in the Atlantic, Indian, and Pacific Oceans. It is glassy, exces- LARVA OF Cavo- 

 sively thin, somewhat cylindrical, but produced posteriorly to an linia gibbosa. 



Cavolinia tridentata. 



