REPORT ON THE PTEROPODA. 
91 
On the other hand, Souleyet 1 expresses his belief that Hyalaea depressa is only a 
young state of Ccivolinia inftexa. This opinion 2 seems to me correct. In fact my 
examination of a specimen of Hyalaea depressa showed me that this form was sexually 
immature, with incompletely developed accessory genital glands, "while on the other hand 
the slight thickness of the shell, the length, the comparative narrowness, and the 
curvature of the posterior portion, are in favour of Souleyet’s theory ; and besides, 
Hyalaea depressa has been found almost always where Cavolinia infiexa occurred in 
abundance, namely, in the Pacific Ocean, 20° S., 87° AV. (d’Orbigny), 5° N., 115' W.; 
Callao to Honolulu (“Yettor Pisani” Expedition, June 9, 1884); in the Indian Ocean, 
Colombo to Aden (“Yettor Pisani’’ Expedition, March 10, 1885); and, finally, in the 
Atlantic (Challenger Expedition). 
Challenger Specimens. — I. Living specimens. 
Station 216 a, February 16, 1875; Samboangan to New Guinea; lat. 2° 46' N., 
long. 134° 11' E. 
On May 4, 1875 ; at Yokohama. 
Station 350, April 11, 1876; Ascension Island to St. Vincent; lat. 10° 55' N., 
long. 17° 46' W. 
II. Deposit shells. 
Station 219, March 10, 1875; Admiralty Islands to Yokohama; lat. 1° 54' 0" S., 
long. 146° 39' 40" E.; depth, 150 fathoms ; bottom, coral mud. 
There remain four other names, which are not mentioned by Boas, viz., 
Hyalaea truncata, Lesueur . 3 Cleodora trijilis, Troschel . 5 
Hyalaea rugosa, S! Oibigny* (JBalantium Pleuropus hargeri, Verrill . 6 
rugosum, Gray). 
Souleyet 7 refers the two former to his “ Cleodora curvata .” This appears to me 
inaccurate. Hyalaea rugosa (which has been found in the South-east Pacific) differs 
from “ Cleodora curvata ” in being less thick, in being longer in proportion to breadth, 
and in having a less marked curvature. 
I regard this form and Pleuropus hargeri (North-west Atlantic) as two successive 
stages of Cavolinia gibbosa. The length, the slight thickness, the moderate curvature 
of the initial point in both forms, as well as the slight divergence of the lateral margins, 
support this opinion. 
1 Histoire naturelle des Mollusques Pteropodes, p. 44. 
2 Shared by Weinkauff (Die Conchylien des Mittelmeeres, t. ii. p. 424). 
3 In de Blainville, Hyale, Diet. d. Sci. Nat., t. xxii. p. 82. 
4 Voyage dans l’Amerique m^ridionale, t. v. p. 118, pi. viii. figs. 12-14. 
6 Beitrage zur Kenntniss der Pteropoden, Archivf. Naturgescli., 1854, Bd. i. p. 205, pi. viii. fig. 4. 
6 Catalogue of the Mollusca added to the Fauna of New England during the past ten years, Trans. Connect. Acad., 
vol. v. p. 555. 
7 Histoire naturelle des Mollusques Pteropodes, p. 52. 
