115 
several pecs of the same genus occur in the Corniferous Limestone. The latter formation 
also contains examples of the genera Platyostoma, Strophostylus, Holopea and possibly Helico- 
toma. 
Genus PLATYCERAS (Conrad). 
“Shells depressed, sub-globose, sub-ovoid, or obliquely sub-conical. Spire small; volu- 
tions few, sometimes free and sometimes contiguous, without columella; aperture more or less 
expanded, often campanulate and sometimes with the lip reflexed ; peristome entire or sinuous. 
Surface striated or cancellated, often spirally ridged or plicate, and sometimes strongly lamel- 
lose transversely, nodose or spiniferous.”—(Hall, Pal. N. Y., Vol. IL1., p. 309). 
The shells of the genus Platyceras are readily recognised by their obliquely spiral or 
straight shape, their wide aperture, their usually or always having a sinus in the outer lip, 
and the absence of a columella. They may be dextral or sinistral. The genus is identical 
with Acroculia (Phillips) over which it has the priority, and appears to be most nearly allied 
to the recent Capulus. 
The following species of Platyceras occur in the Corniferous Limestone and Hamilton 
formation of Western Ontario ; but their determination is rendered uncertain by the imper- 
fect and ill-preserved condition in which they are found. 
138. PLATYCERAS VENTRICOSUM (Conrad). 
Platyceras ventricosum (Conrad), Ann. Rep. Pal. V. Y., 1840, p. 206. 
Platyceras ventricosum (Hall), Pal. N. ¥., Vol. III, Pl. LVI., Figs. 1,4 & 8, and Pl. 
LVII, Fig. 4. 
Platyceras ventricosum (Meek and Worthen), Geology of Illinois, Vol. III, Pl. XI, Figs. 
Dyn 
Shell obliquely ovate, composed of two and a half or three volutions of which the last is 
extraordinary expanded and ventricose. The spire is depressed below the plane of the upper 
side of the body-whorl, and the inner lip is in contact with the spire. The surface is marked 
by fine transverse striz, and near the aperture by coarse undulating lines or folds of growth. 
I have one or two specimens, of which one is figured in pl. II., fig. 1, which consist of 
the body-whorl of alarge Platyceras almost certainly to be identified with P. ventricosum. None 
of our examples, however, exhibit the spire. 
Locality and Formation.—Corniferous Limestone of Port Colborne. 
139. PLATYCERAS INTERMEDIUM (Hall) ? 
(Plate IT., Fig. 2.) 
‘ Shell arcuate, sub-spiral, making little more than two volutions, the last one free and 
becoming gradually straight. The apex is very minute, consisting of little more than a single 
volution, with the parts Closely contiguous, Surface marked by fine lamellose transverse strive, 
, which are slightly undulated upon the body of the shell. ”__ (Hall, 
PabiN.Y Viele iih ps 32t, PLiLVIne., FigsTL) 
I possess two examples of the body-whorl of a species of 
Platyceras from the Corniferous Limestone, of which all I can as- 
sert is that they are of the type of P. intermedium (Hall), if not 
absolutely belonging to the same species. Both consist of the 
slightly curved and greatly expanded body-whorl, the lip of the 
aperture being markedly undulated, and the surface exhibiting 
numerous close-set transverse striz, which are undulated to cor- 
respond with the sinuous aperture, and are very closely arranged 
near the aperture is nearly round. 
Locality and Formation.—Corniferous Limestone of Port 
Fig. 51. Colborne. 
Body-whorl of a species of Platy- 
ceras apparently identical with P. 
intermedium (Hall). From the 
Corniferous Limestone. 
