428 CRETACEOUS GASTROPODA 
cylindrically globose, thin, narrower posteriorly, with a short flattened spire, more 
inflated anteriorly; with an enlarged aperture, an insinuated, thin and slightly 
twisted inner lip. 
The shells of the former genus are said to differ by being more opaque and 
covered with an epidermis, while those of Diaphana are hyaline; there also are 
slight differences in the animal, and the former appears more to resemble Cylichna 
than Diaphana, still I think that further observations on the animals would be 
very valuable, so as to be certain of knowing whether the distinctions pointed 
out are really of generic difference; the shells do not appear to be generically 
different. Iam not acquainted with any fossil species of the two genera. 
3. Cylichna, Loven, 1846 (ibid., p. 9). Shell solid, sub-cylindrical, convolute, 
posteriorly attenuated and truncated, anteriorly somewhat thickened, inner lip 
conspicuously thickened anteriorly, twisted or with a distinct fold. 
H. and A. Adams state that the animal of Cylichna has not central teeth, 
but Loven figures the teeth of C. alba as consisting of one central, one pair of 
large inner lateral, and five small outer lateral. Meyer and Mobius (Hinterkiemer- 
der Kieler Bucht., p. 87) state that Cy. truncata, Montague, has no radula, but a 
gizzard with strong plates. Farther observations regarding the dentition are, 
therefore, very desirable. The recent species of Cylichna* are rather numerous, 
and the genus is also numerously represented among fossil shells, though the 
species are occasionally very difficultly distinguished from those of Bullina 
(= Tornatina), when the latter have the spire flattened or even somewhat im- 
pressed. The species first appear in the Trias, and continue to occur through 
all the successive formations; those of the cretaceous beds will be mentioned 
subsequently. 
4, Volvula, Adams, 1850 (ibid., p. 14) is distinguished from Cylichna in 
having the posterior end not truncated, but pointed and produced; there is 
one distinct anterior columellar fold present. Several recent species have been 
described by A. Adams from the Japan seas in Ann. mag. nat. hist., 1862, IX, 
pp. 154-155. <A. Adams dredged his specimens from 25-63 fathoms. Fossil 
species are not common in tertiary deposits, and the oldest known one is from the 
cretaceous. : 
5. <Acteonella, d’Orbigny, 1842 ( Volvulina, Stol., 1865, Sitzb. Akad., Wien, 
LIT, p. 519). Shell convolute, like Volvula, attenuated at both ends, aperture linear, 
inner lip anteriorly thickened and provided with three folds. The shells which as 
yet are only known from cretaceous deposits mostly closely resemble the recent 
Volvula, differing from it merely by the presence of three columellar folds on 
the anterior portion of the inner lip. The animal of Volvula has as yet not been 
observed, but A. Adams, who examined all the known recent species, states that 
the shell is closely allied to that of Cylichna, and it is on this account that we 
not only retain the genus Volvula in the sub-family Cyrzzcuyrv2, but also add 
* A large number of new Japanese species is described by A, Adams in Ann. mag. nat. hist., IX, 1862, 
p- 150, etc. 
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