368 



MOLLUSCS. 



ably. The mouth, lips, and tentacles are the same as in Limadna. Three genera 

 are comprised in this family, namely, Clio, Cuvierina, and Cavolinia. Clio 

 is subdivided 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 trans- 

 verse grooves and ridges. H. striata, the only known species of this genus, is 

 cosmopolitan. Styliola has a slender tapering 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 recognisable. The 

 genus commonly known as Cuvieria contains 

 only a single species (C. columnella), which 

 has been obtained in the Atlantic, Indian, 

 and Pacific Oceans. It is glassy, excessively 

 thin, somewhat cylindrical, but produced 

 posteriorly to an acute point. This narrowed 

 portion is generally wanting in adult shells. 

 In the soft-parts it closely resembles Clio, 



and it is chiefly on conchological grounds that it is separated. The genus Cavolinia 

 is perhaps the commonest of all. The shell is generally pale horny brown, often 

 globose, composed of a ventral and dorsal plate, which are united inferiorly, but 

 not along the sides or above. The dorsal piece is flattish, and the ventral generally 

 very globose. The shell is produced into a spine behind, and the 

 sides generally terminate posteriorly in sharp points or spines. 

 The animal somewhat resembles Clio in its external characters, 

 but is remarkable for the presence of lateral prolongations of the 

 mantle, which project through the lateral slits in the shell. 

 Eight species are recognised by Dr. Pelseneer. C. tridentata, C. 

 uncinata, C. globosa, and C. trispinosa are the best known. 



In the family Cymbuliidce the shell is very different from 

 that of other Thecosomata. It is cartilaginous or gelatinous, 

 bilaterally symmetrical, and somewhat resembles a slipper in 

 general form. It is very easily detachable from the animal, and consequently a 

 number of species, which in reality belong to this family, have been characterised 

 as shell-less. Pointed at the ventral extremity and truncated at the dorsal 

 end, it is covered with acute spine-like tubercles arranged in longitudinal series. 

 The modified foot, or fins, are large and rounded. The animal is furnished with 

 a radula. Of Cymbulia, two species are known. C. peroni is common in the 



Cavolinia tridentata. 



LARVA OF Cavolinia 



