REPORT ON THE PTEROPODA. 
87 
As to the remaining eleven titles, the last author who has given a systematic account 
of Pteropods, namely Boas, mentions seven of them which he regards as representing 
adult forms and distinct species. These are : — 
] . Cleodora compressa, Souleyet. 
2. Cleodora pygmsea, Boas. 
3. Cleodora curvata, Souleyet. 
4. Pleuropus longijilis, Troschel. 
5. Hyalsea rotundata, Boas. 
6. Hyalaea Isevigata, d’Orbigny. 
7. Hyalsea depressa, d’Orbigny. 
It is necessary to examine these forms individually. 
# 1. Cleodora compressa, Souleyet. 
1850. Clio depressa, Gray, Catalogue of the Mollusca iu the Collection of the British Museum, 
pt. ii., Pteropoda, p. 14 ( sine descriptione). 
1852. Cleodora compressa , Souleyet, Voyage de la Bonite, Zoologie, t. ii. p. 181, pi. vi. 
figs. 26-32. 
From Souleyet’s figure it may be inferred that this Pteropod did not exhibit fully 
developed reproductive organs, and was not therefore an adult. 
The form in question ought to be referred to Cavolinia trispinosa. To this view, 
formerly suggested by Pfeffer, 1 Boas objects that in Cleodora compressa the mouth is 
narrower, and that in proportion to the height Cavolinia trispinosa is thicker than 
Cleodora compressa. But these comparisons only hold true with a Cleodora compressa 
which is much flattened and a swollen Cavolinia trispinosa, and are not sufficient to 
disprove our opinion, which is based on the following facts : — 
1. The embryonic portion, the general form of the shell, and the curvature of the 
sides are identical in Cleodora compressa and Cavolinia trispinosa. 
2. The fins and the posterior lobe of the foot in Cleodora compressa have absolutely 
the same form as in Cavolinia trispinosa. 
3. The dorsal surface of the shell of Cleodora compressa exhibits three ridges 
disposed in exactly the same way as in Cavolinia trispinosa, and not as in the genus Clio 
{Cleodora). 
4. As concerns geographical distribution, the two forms are equally cosmopolitan. 
Like Souleyet and Boas, the palaeontologist Searles Wood 2 has regarded the 
young fossil Cavolinia trispinosa as a distinct species which he has named Cleodora 
infundibulum. 
Habitat. — “ Cleodora compressa ” has been noted in the Atlantic Ocean (Souleyet, 
Pattray) and also in the Pacific Ocean (“ Vettor Pisani” Expedition). 
1 Uebersicht der auf S.M. Schiff Gazelle und von Dr. Jagor gesammelten Pteropoden, Monatsber. d. k. preuss. Akad. 
d. Wiss. Berlin , 1879, p. 237. 
2 Catalogue of Shells found in the Crag, Ann. and Mag. Nat. Hist., ser. 1, vol. ix. p. 459, pi. v. fig. 13, 1842. 
