92 
THE VOYAGE OF H.M.S. CHALLENGER. 
As to “ Cleodora trijilis,” it is difficult to determine to what adult form this young 
stage should be referred. But the absence of any well-marked constriction separating the 
embryonic shell, and the presence of three lateral appendages on each side of the mantle, 
show clearly that we have here to do with a Cavolinia and not with a Clio {Cleodora). 
But according to Troschel the posterior portion of the shell is not eurved, while all the 
species of Cavolinia (except the group Cavolinia trispinosa and Cavolinia quadridentata, 
where the embryonic shell is markedly separate) exhibit a dorsal curvature of the initial 
portion. The position of “ Cleodora trijilis ” must therefore remain uncertain. 
Family III. Cymbulii dm. 
1841. Cymbulidse , Cantraine, Malacologie mcditerraneene etlittorale, Mem. Acad. Sci. Bruxelles, 
t. xiii. p. 33. 
Hyalseidse, pars, Auctorum. 
1885. Alata, Wagner, Hie Wirbellosen des weissen Meeres, Bd. i. p. 119. 
Characters. — “ Shell ” straight, bilaterally symmetrical, so-called cartilaginous, quite 
enveloped in the mantle. The animal cannot completely retire within it. The 
animal has a ventral pallial cavity, and the fins form a broad disc, on the dorsal 
margin of which the cephalic portion is laid back. 
Description. — The “ shell ” of the adult Cymbuliidse is considerably elongated in a 
dorso-ventral direction. It is somewhat hollowed out in the form of a boot or slipper, 
and is more or less broadly open ventrally. It is not homologous with the calcareous 
shell of other Thecosomata. In the Cymbuliidse the homologue of the latter falls off at 
the close of the larval life. As to the cartilaginous “ deutoconch ” or “ pseudoconch,” it 
is the result of thickening of the integument. Nor is it the only illustration of such a 
structure among the Thecosomata, for in Cavolinia tridentata, on the anterior portion of 
the dorsal lip of the shell, there is a small covering portion with the same structure as 
the “ shell ” of the Cymbuliidse, and similarly produced by the mantle, the prolongations 
of which may cover a considerable portion of the shell. 
The deutoconch of the Cymbuliidse, which is only covered by a delicate epithelial 
layer, is very readily lost , 1 as the result of which the members of this family have often 
been described as naked. 
The animal has its visceral portion relatively little developed, and the foot, modified 
as a fin, greatly predominates. The cephalic portion is distinct ; it extends beyond the 
dorsal margin of the fin, and is reflected on the anterior portion of the latter, forming 
a sort of proboscis, more or less elongated, sometimes remaining free {Gleba and 
Cymbidiopsis ) or fixed to the surface of the fin. The lips do not consist as in the 
typical Thecosomata (Cavoliniidse) of two dorso-ventral folds, united dorsally above the 
mouth, and continued on divergently to the ventral margin of the fins without re-uniting 
1 By “ Cymbulia ” ovata, Quoy and Gaimard, Gleba cor data, Forskal, &c. 
