THE 
GEOLOGICAL MAGAZINE. 
NEV) seRIES, DECADE. Tl. VOL. VII. 
No. IIL—FEBRUARY, 1880. 
ORIGIN AD: ARTICLES. 
I.—Creracrous GASTEROPODA. 
By J. Srarxre Garpner, F.G.S., M.G.S. France. 
(PLATE III.) 
N September, 1875, Decade II. Vol. II. p. 894, of this Macazrnn, 
I was enabled, after having previously described them in detail,! 
to group all the known British Cretaceous Aporrhaide together into 
four genera; and in March, 1876,’ I added a fifth genus. 
Mr. J. F. Walker, M.A., F.G.S., having kindly forwarded to me 
for description a few new Gasteropoda from Upware, including two 
Aporrhaide, I now avail myself of the opportunity, in noticing them, 
to revise my previous work. Although collecting from the Gault 
and Grey Chalk of Folkestone (both of which deposits are very rich 
in species) has been incessant since 1875, no new forms have been 
found; and with the exception of those from Upware, none have 
been met with in any Cretaceous rocks in England. 
The revision required is due, with a trifling exception, to the fact 
of my having overlooked certain genera established in America by 
MM. Conrad, Gabb, and Meek. 
In the first place, I find it necessary to abandon the genus Orni- 
thopus. A genus, Tessarolax, was established so long ago as 1864 
by Gabb in the Paleontology of California, vol. i. p. 126, which he 
defined as follows :— 
Shell fusiform, spire and aperture about equal; spire incrusted by a thin deposit 
so as to obliterate the sutures. Body-whorl with two varix-like processes. Aperture 
broad above, continued below in a long curved canal; a posterior canal continues 
for some distance up the spire. Columella incrusted, without folds or teeth. Outer 
lip possessing two spine-like canals. 
This embraces substantially all the characters of Ornithopus, with 
the addition of the varix-like processes and thin incrustation of the 
spire. These, however, can hardly be considered characters of suffi- 
cient importance, to render a separate genus desirable for shells 
not possessing them. In 1868, indeed, Gabb seems to have been of 
this opinion, for he modified the generic characters, and claimed 
Pterocera bicarinata, D’Orb., as a typical species. Yet in 18695 
he appears to have again changed his mind, for we find two species 
almost identical with P. bicarinata of d’Orb. expressly excluded, and 
1 GronocicaL Macazine, Decade II. Vol. II. pp. 49, 124, 198, 291, 393. 
2 Ibid, Decade II. Vol. III. p. 160. 
3 Paleontology of California, vol, ii, p. 166. 
DECADE II.— VOL. VII.—NO. II. 
