■REPORT OX THE PTEROPODA. 
89 
As to the species to which this young form should be referred, the slight curvature of 
the lateral margins leads me to believe that it belongs to a species in which the posterior 
portion is relatively much developed ; and the great breadth of this region in proportion 
to its length, as well as the absence of dorsal ribs, lead me to regard Cleodora curvata 
as simply a young stage of Cavolinia uncinata. It may he further noted that Cleodora 
curvata has only been found in the Atlantic where Cavolinia uncinata is most abundant. 
To his Cleodora curvata Souleyet 1 referred Hyalaea rugosa, d’Orbigny. But the 
latter appears to me to differ considerably in being less thick, in having a proportionately 
greater lensth, and in exhibiting a less marked curvature. 
Finally, the form described by Huxley under the title Cleodora curvata is not a Clio 
at all, since Huxley himself speaks 2 of the “shell fissured laterally,” and of the “filiform 
appendages of the mantle.” It is also a Cavolinia, but differs from the Cleodora curvata 
of Souleyet, and corresponds to Hyalaea depressa, d’Orbigny (see below). 
4. Pleuropus longifilis , Troschel. 
1854. Pleuropus longifilis , Troschel, Beitrage zur Kenntniss der Pteropoden, Archiv f. 
Katurgesch., Jalirg. xx. Bd. i. p. 208, pi. viii. figs. 1, 3. 
1855. Hyalsea complanata, Gegenbaur, Untersuchungen fiber Pteropoden und Heteropoden, 
pp. 40, 211, pi. i. fig. 1. 
1886. Hyalsea longifilis, Boas, Spolia atlantica, p. 128, pi. iv. figs. 64, 65. 
Cantraine has already recognised in this form (which he identified with Hyalsea 
laevigata, d’Orbigny) the young stage of Cavolinia tridentata. It is to this species 
that one must refer the forms described by Troschel and Gegenbaur. 
At the suggestion of Dr. Paul Schiemenz, I took occasion at Naples to examine 
numerous specimens of Hyalaea tridentata, among which I could note all the transitions, 
in size and thickness, between Pleuropus longifilis and the typical adult Cavolinia 
tridentata. I also observed that the stage longifilis might be abnormally prolonged 
to a late period, and then developed into specimens of large size and flattened form, 
with the closing apparatus not yet developed, and with the reproductive system still 
immature. 
5. Hyalaea rotundata, Boas. 
1886. Hyalsea rotundata, Boas, Spolia atlantica, p. 129, pi. iv. figs. 59-61. 
This form is certainly the young stage of Cavolinia globulosa. That this is so is 
sufficiently demonstated by the following characters common to the two forms : — 
1. Dorso- ventral dilation of the shell ; 
1 Histoire natuielle des Mollnsques Pteropodes, p. 52. 
2 On the Morphology of the Cephalous Mollusca, Phil. Trans., 1853, p. 42. 
(ZOOL. CHALL. EXP.— PART LXV. 1887.) 
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