117 
smaller than the typical forms of P. dumosum, and also carries much fewer spines. Upon the 
whole it seems to be most like P. dumosum, var. rarispinum, Hall (Fifteenth Report on the 
State Cabinet, . 38), though it never appears to attain anything like such a size. It al 
somewhat resembles P. dumosum, var. attenuatum, Meek (Paleontology of Ohio, Vol. I. 
Pl. XX., Figs. 2 a, 6.) 
The shell in our specimens is always of small size, 
never appearing to exceed three quarters of an inch 
in length, and is composed of about two volutions. 
The apex is small, closely enrolled, and in contact 
with the body-whorl till close to the aperture. The 
body-whorl is greatly expanded, the aperture patu- 
lous, oval, or rounded, with a diameter of about half 
an inch, and having the lip strongly sinuated. The 
surface is marked with fine close-set transverse stria, 
which are stronger and are undulated towards the 
Rie aperture. The body-whorl carries eight to twelve or 
erent ies oa al) from the Hamilton More strong tubular spines, which are arranged in 
Formation. Natural size. somewhat irregular longitudinal lines. It is quite 
possible that our shells are new, as they do not appear to correspond exactly with any previ- 
ously recorded form ; but, in the present condition of the genus Platyceras, it would be 
unsafe to give it a separate title. 
Locality and Formation.—Common in the Hamilton Formation, Arkona, Township of 
Bosanquet. 
Genus PLATYosToMA (Conrad). 
The shells of this convenient but hardly definable genus are ventricose, with a short, 
depressed, or very moderately elevated spire, and an extremely expanded body-whorl. The 
aperture is very large, and the columellar lip thickened. 
Specimens which appear to have all the characters of P. ventricosa (Conrad), from the 
Lower Helderberg and Oriskany Sandstone, are not uncommon in the Corniferous limestone 
of Ontario; but they occur entirely in the condition of casts, and do not, therefore, permit of 
anything further than their mere identification. ' 
144, PLATYosTOMA VENTRICOSA (Conrad). 
(Plate IT., Fig. 4.) 
Platyostoma ventricosa (Conrad), Jour. Acad. Nat. Sci., Philadelphia, Vol. VIIL., 
p. 275. 
Platyostoma ventricosa (Hall), Pal. N. Y., Vol. III., p. 300, Pl. LV., and p. 469, Pls. 
CXII., CXIII. and CXV. 
‘‘ Shell globose, or depressed globose, and often obliquely ovoid, varying in form. Spire 
moderately elevated, consisting of three or four volutions, the last of which is extremely ven- 
tricose : volutions flattened upon the upper side; aperture circular or subovate ; columellar 
lip reflexed. Surface marked by fine closely arranged striz parallel to the lines of growth.” 
(Hall, Joc. cit., p. 469.) 
Casts apparently belonging to this species are far from uncommon in the Corniferous 
Limestone of Ontario, and I have figured one of the best that I have seen (Plate II., fig. 4). 
In form and dimensions the specimens differ considerably, but they all agree in the moder- 
ately elevated spire, ventricose body-whorl, and simply striated surface. The specimen 
figured has the body whorl less convex below than is usual in this species as figured by Hall, 
and its dimensions are as follows:—Height one inch and a half (in reality somewhat over 
this) ; breadth two inches and two lines; height of aperture, sixteen lines; width of aperture, 
-seventeen lines. Many of the examples, however, have dimensions smaller than the above. 
Locality and Formation.—Corniferous Limestone, Port Colborne. 
Genus STROPHOSTYLUS (Hall), 
Shell with a depressed or moderately elevated spire, and an expanded and ventricose 
