76 
THE VOYAGE OF H.M.S. CHALLENGER. 
however, no warrant for this opinion. Cavolinia injlexa certainly belongs to the second 
Subgeneric section of Cavolinia, including the more typical or more highly specialised 
forms, all, in fact, except Cavolinia trispinosa and Cavolinia quadridentata. Its 
elongation and its flattening are not a whit more extraordinary than the expansion and 
shortening of Cavolinia globulosa. 
From the above observations this results, that the huge list of species is reduced by 
analysis to eight, and that, without going to an extreme like d’Orbigny, who united 
all the Thecosomata of the family Cavoliniidse into a single genus Hyalaea, it may be 
said that at least the eight species above mentioned form a tolerably homogeneous unit 
within a single genus. 
The eight species thus allowed to exist may be distinguished in the following 
fashion : — 
Key to the Species. 
I. Dorsal lip thickened into a pad. 
1. Shell with lateral points, ..... 
2. Shell without lateral points, .... 
II. Dorsal lip with a thin margin. 
1. Posterior portion of the ventral lip markedly projecting laterally, 
2. Ventral lip not more developed than the dorsal. 
A. Shell without appreciable lateral points. 
a. Shell narrower at the end of the lips than anteriorly. 
a. Ventral surface rounded, . 
/?. Ventral surface with an anterior transverse keel, 
b. Shell as broad at the end of the lips as anteriorly, 
B. Shell with distinct lateral points. 
a. Upper lip flattened posteriorly, . 
b. Upper lip directed straight forwards, 
Cavolinia trispinosa. 
Cavolinia quadridentata. 
Cavolinia longirostris. 
Cavolinia globulosa. 
Cavolinia gibbosa. 
Cavolinia tridentata. 
Cavolinia uncinata. 
Cavolinia injlexa. 
The best series of figures of these eight species is undoubtedly that given by Boas. 1 
We shall, therefore, refer to these figures, since it is useless to figure afresh species 
already sufficiently well known, and hopeless to expect better figures than those of Boas. 
# 1. Cavolinia trispinosa (Lesueur). 
1821. Hyalxa trispinosa, Lesueur, MS. in de Blainville, Hyale, Diet. d. Sci. Nat., t. xxii. p. 82. 
1827. Hyalxa mucronata, Quoy et Gaimard, Observations Zoologiques faites a bord de 
1’ Astrolabe, &c., Ann. d. Sci. Nat., ser. 1, t. x. p. 231, pi. viiiB, 
figs. 1, 2. 
1832. Hyalxa depressa, Bivona, Descrizione di una nuova specie di Jale, &c., Efemeridi 
scientifiche e litterarie per la Sicilia, p. 57, pi. i. figs. 4, 5. 
1841. Hyalxa cuspidata, Delle Chiaje, Descrizione e notomia degli animali senza vertebre del 
Regno di Napoli, pi. clxxx. figs. 1, 2 ( non d’Orbigny). 
1 Spolia atlantica, pi. i. figs. 3-11 ; pi. ii. figs. 14-21. 
