252 CRETACEOUS GASTROPODA 
his triassic Platystoma Suessi. This remarkable shell,—which must receive a new 
generic name,—is, in incomplete specimens, hardly to be distinguished from Disco- 
helix, but in reality the outer lip was expanded into a large irregular wing, and the 
apertural margins were united and circular, the aperture itself being suddenly 
deflexed, so as to have its plane parallel to the discoidal form of the shell. It cannot 
be denied, that some of the species of Discohelixv may be shown to belong to the 
same genus as the Platystoma Suessi, Hornes, but there are already several cases 
known, where the aperture of Discohelix has been observed, so as fully to guarantee 
its generic independence. It would besides be hardly advisable to suppose, 
that all the numerous species of known Discoheliv are only immature specimens. 
The small size of the triassie shell would give little support to such an idea. It 
is difficult to say anything about the classification of the Plat. Suessi, as the form 
of the aperture excludes it from this family. I am not acquainted with any 
other form, to which the expansion of the outer lip could be even remotely com- 
pared, than to that of some species of Onustus and Cirsotrema. 
3. Cyclogyra, Wood, 1842 (Ann. Mag. Nat. Hist., Vol. IX, p. 458, pl. 5, 
fig. 5),—Planaria, Brown, not Linn. and others,—Discohelix, apud H. and 
A. Adams, Chenu and others. 
Wood proposed this genus for a small, orbicular, discoidal, and smooth shell, 
composed of numerous depressed volutions, being rounded at the periphery, and each 
succeeding one embracing partially the previous. It seems to us, that this genus 
ought to be retained in this very same sense, as originally proposed for the little 
shells named Planaria by Brown and other species, like the recent Orbis foliaceus 
of Philippi. Lea described several tertiary species from the Alabama eocene 
deposits, and others are reported in different works. I must here again refer to the 
fossil Cornuspire, for I believe many described as such are not Foraminifera, but 
Gastropoda. 
Wood, when instituting the genus, says, that it may belong to the /zruzTIDx, which classi- 
fication is not at all improbable. I do not know the details of the organisation of Orbis foliaceus, 
Phil., but it is certain, that the form of the shell very much recalls some species of Burtinedla, and 
possibly the genus may be better placed in the VERwe7Ips. 
The only cretaceous species, which I think is a true Cyclogyra, is the Cycl. (Discoheliz) Leana, 
Gabb (Pal. Calif. 1864, I, p. 119, pl. 20, fig. 75,) from the cretaceous Californian deposits. 
4. Ophileta, Vanuxem, 1842, (Hall. Pal., New York, I, p.11, pl. 3, figs. 4-6) 
has been proposed for a few discoidal smooth shells, composed of very nwmerous 
whorls. It is quite impossible to regard this characteristic as of any importance 
for the present. The two paleozoic species, O. levata and complanata, which had 
been described only from very imperfect specimens, are in fact nothing more than 
discoidal Straparolus or Discohelix; the first named has the whorls keeled only 
below, the second apparently on both margins of the periphery, above and below. 
The strize of growth have not been observed. 
5. Lecyliomphalus, Portlock, 1843, (Geol. Rep., ete., p. 411,—Serpularia, 
Romer, 1848, non Mimst.) has the whorls generally coiled in one plane, or nearly so, 
and dissolute, as in an Ancyloceras. ‘The strive of growth are not perceptibly bent 
