39 
surface rounds suddenly and then descends abruptly to the lateral mar- 
gins. The entire surface is covered with fine, rounded, flexuous cost®, 
from eight to ten of which occur in a distance of 5 mm. towards the front 
of the valve. No spines were noted. This species is distinguished from 
P. cora of the Pennsylvanian in being more narrowly rounded transversely; 
the change from the gently convex median part to the lateral slopes is more 
sudden and the lateral slopes are more abrupt. 
A brachial valve resembles this Bpecies in the character of the cost®, 
in the strong concentric wrinkles upon the ears which become less strong 
over the median part of the valve, and in the sharp delimitation of the ears. 
It differs in its very slight concavity, about 2 mm. in a length of 25 mm.; 
the usual valve of this specieB is highly concave. 
Locality and Horizon. Throughout the Mississippian of the Mississippi 
valley. In the Minnewanka region in the Lower Mississippian of section 
2-32 (R), 34 (?). 
Productus fernglenensis Weller 
1909. Productus fernglenensis Weller, Bull. Geol. Soc. Am., vol. 20, p. 299, 
PL 12, figs. 14-17; Weller, 1914, 111. Geol. Surv., Mon. 1, p. 106, 
PI. 9, figs. 11-17. 
Locality and Horizon . In the Lower Mississippian (Kinderhook) of 
Missouri. In the Minnewanka region in the Lower Mississippian of sec- 
tion 2-22 (r), 23 (c), 24 (c), 25 (c), 27 (?), 29 (R). 
Productus gallatinensis Girty 
1899. Productus gallatinensis Girty, U.S. Geol. Surv., Mon. 32, p. 533, 
PL 68, figs. 7 a-c, 11 a-d. 
Remarks. The Minnewanka form agrees fully with a suite of this 
species from the Madison limestone of West Gallatin canyon, Montana. 
We are not so persuaded, however, that it is identical with the form de- 
scribed under the same name from the Pennsylvanian of Colorado. This 
latter form, if we may judge from the figures, has a more distinct median 
sinus in the pedicle valve and stronger concentric wrinkles, especially over 
the top of the umbonal region. Such slight differences could, however, be 
of specific importance only upon stratigraphic grounds. The form from 
the basal Pennsylvanian (Morrow group) of Arkansas and Oklahoma, 
described by Mather, 1 is apparently more closely related to the Penn- 
sylvanian form than it is to that from the Madison. As Girty and Mather 
have suggested, this Pennsylvanian form may prove to be P. boonensis 
Swallow. Productus arcualus Hall from the Kinderhook of the Mississippi 
valley has weaker, less numerous, and less regular stri®. 
Locality and Horizon. Lower Mississippian of Yellowstone National 
park and Montana. In the Minnewanka region in the Lower Mississippian 
of section 2-22 (C), 23 (r), 24 (c), 25 (C), 29 (r), 34 (r), 35 (?). 
1 Bull. Sci.Lfib., Denison Univ., vol. 18, p. 163. 1918. 
