6 
Family, placenticepatidae 
Genus, Placenticeras Meek 
Placenticeras meeki J. Boehm 
Placenticeras placenta (deKay) (part.) 
F. B. Meek: U.S. Geol. Surv., Terr., vol. IX (1876), pp, 465-468, 
PI. 24, fig. 2. 
Geol. Surv., Canada, numerous reports on western Great Plains. 
Placenticeras meeki J. Boehm 
J. Boehm: Deutsche Geol. Gesell. Zeitsche., vol. L (1898), p. 200 
(footnote) . 
J. B. Reeside, jun.: U.S. Geol. Surv., Prof. Paper 151 (1927), pp. 29-30, 
PI. 22, figs. 5-7; Pis. 23-24; PI. 25, figs. 1-2. 
Placenticeras whitfieldi Hyatt 
A. Hyatt: U.S. Geol. Surv., Mon. 44, pp. 221-232, PI. 45, figs. 3-16; 
PI. 46; PL 47, figs. 1-4 (1903). 
A. W. Grabau and H. W. Shimer: North American Index Fossils, 
vol. II (1910), p. 218, figs. 1493-1494. 
In some specimens, on being broken down, lines of tubercles may 
be seen on the young shell. These are all small and are generally absent 
on the larger volutions. Hyatt, in one place^ regards them as merely 
individual reversions to the primitive type, but in the specific description* 
refers them to a variety ‘‘tuberculatum” j stating them to be intermediate 
between this species and P. intercalare. 
The species can be distinguished from P. placenta of the Atlantic 
Cretaceous by certain characters which, however, can be observed only 
in comparing the two species. The venter is narrower throughout life 
and becomes less completely rounded in the gerontic stage. This rounding 
also comes at a much larger size than in P. placenta. Tubercles are lacking 
in the typical forms, but when present are small, whereas those of P. 
placenta are large and elongated, much coarser, and less numerous. The 
suture is also more complex and sinuous than that of the eastern form. 
Of the specimens preserved in the Bearpaw collection, the largest 
specimen, when complete, had a greater diameter of 365 mm. and a width 
of 75 mm. 
Occurrences, (1) East side of Oldman river, sec. 20, tp. 8, range 22, 
W. 4th mer. (2) Immediately north of the old Canadian Pacific Railway 
bridge over St. Mary river. Fox Hills, lower shalo — Cypress lake. 
Collector, M. Y. Williams. 
(3) Coulee, west of road 3| miles south of Irvine, Alberta. 
(4) Sec. 22, lot 9, range 23, W. 4th mer., Oldman river. (5) Sec. 1, lot 11, 
range 3, W. 4th mer., Ross creek. (6) Mid-line between SE. and SW. | 
sec. 25, lot 9, range 6, W. 4th mer. Collector, W. S. Dyer. 
*Hyatt, A.: U.S. Geol. Surv., Mon. 44, p. 190 (1903). 
*Hyatt, A.: U.S. Geol. Surv., Mon. 44, pp. 211, 232 (1903). 
