3 68 
MOLLUSCS . 
ably. The month, lips, and tentacles are the same as in Limacina. 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 Cwvieria contains 
only a single species ( Ccolumnella), 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 interiorly, 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, G. 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 
gibbosa. 
