115 



several species 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. ILL, 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 ventrkosum (Conrad), Ann. Rep. Pal. N. Y., 1840, p. 206. 



Platyceras ventrkosum (Hall), Pal N. Y., Vol. Ill, PI. LVI., Figs. 1, 4 & 8, and PL 

 LVII, Fig. 4. 



Platyceras ventrkosum (Meek and Worthen), Geology of Illinois, Vol. Ill, PL XI, Figa. 

 4a, b. 



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 striae, and near the aperture by coarse undulating lines or folds of growth. 



I have one or two specimens, of which one is figured in pi. II., fig. 1, which consist of 

 the body-whorl of a large 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 II. , 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 lauicllose transverse striae, 



which are slightly undulated upon the body of the shell." (Hall, 

 Pal. N.Y., Vol. Ill, j). 321, PL LVIII., Fig. II.) 



I possess two examples of the body-whorl of a species of 

 Platiict-riiK 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 >|>eeies. 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 striiu, which are undulatad to cor- 

 respond with the sinuous aperture, and are very closely arranged 

 near the aperture is nearly round. 



Lni'ii/i/t/ /mil l''<>nnlit>ii. Corniferous Limestone (if Port 

 Fig. 6i. Colborne. 



Body-whorl of a species (if J'litn/- 

 cerax apparently iil< ntii-;il with /'. 

 inti'riiii'iliiini (ll:ill). rp'in tin' 

 Coniiferous Limestone. 



