36 
Pedicle valve slightly concave from umbo forward; in some smaller 
specimens the umbonal region is flat, the slight concavity beginning an- 
terior to this; the lateral margins, especially towards the cardinal margin, 
are gently convex. Beak very small, extended only slightly beyond the 
cardinal margin. Cardinal area rather narrow, flat, almost at right angles 
to the plane of the valve, inclined slightly posteriorly, its lateral margins 
angular; delthyrium forming almost an equilateral triangle. Internally 
the muscle scars are poorly defined; the teeth are supported by short 
dental plates — merely thickened ridges bordering each margin of the 
delthyrium. 
Brachial valve of moderate convexity, with greatest convexity pos- 
terior to the middle, the surface curving very gently and regularly in all 
directions except towards the cardinal margin where it is more abruptly 
bent downward; the cardinal extremities are slightly flattened. Extending 
from the beak forward is a slight median flattening. Beak inconspicuous. 
Internally the muscle markings are poorly defined; the cardinal process is 
furrowed longitudinally with two grooves, giving to it a somewhat trilobed 
appearance; the dental sockets are very near the beak and well developed. 
Surface of each valve marked by abruptly elevated radiating striae; 
at the anterior part of a mature shell about six occupy the space of 1 mm. 
The striae are often alternating in size; this is more frequently true of the 
brachial valve than of the pedicle. There are also numerous minute con- 
centric growth lines. 
Remarks . This species is known only from separate valves; in no 
case were we able to find it with valves in articulation; but the abundance 
of the two valves, with the practical exclusion of all forms of a similar type, 
makes it certain that they belong to the same species. The form most 
nearly similar to this species with which we could compare it is S. inequalis 
(Hall) from the Kinderhook of Pennsylvania to Utah. The latter is, how- 
ever, somewhat larger and narrower, with less numerous radiating striae 
(Weller gives 2 to 4 in the space of 1 mm.), the pedicle valve is convex or 
flat in the umbonal region and usually for two-thirds its length, and the 
brachial valve has often a faint median sinus. 
Locality and Horizon . In the Minnewanka region in the Pennsylvanian 
of section 2-11 (c), 12 (C). 
Genus, Chonetes Fischer de Waldheim 
Chonetes illinoisensis Worthen 
1858. Chonetes logani Hall, Geol. Surv., Iowa, vol. 1, pt. 2, p. 598, PI. 12, 
figs. 1 a-e, 2 (not C. logani N. and P. 1855) ; Chonetes illinoisensis 
Worthen, 1860, Acad. Sci. St. Louis, Trans., vol. 1, p. 571; Winchell, 
1863, Acad. Nat. Sci. Phil., Proc., p. 5; Winchell, 1865, Acad. Nat. 
Sci. Phil., Proc., p. 116; Meek and Worthen, 1868, Geol. Surv., 
111., Kept., vol. 3, p. 505, PI. 15, figs. 8a, b; Winchell, 1870, Am. 
Phil. Soc., Proc., vol. 11, p. 251; C. loganensis Hall and Whitfield, 
1877, U.S. Geol. Expl. 40th Par., Kept., vol. 4, p. 253, PL 4, fig. 
9; C. illinoisensis Herrick, 1888, Sci. Lab. Denison Univ., Bull., 
vol. 3, p. 35, PI. 3, fig. 21; Herrick, 1890, Geol. Soc. Am., BulL, 
vol. 2, p. 48, PI. 1, fig. 16; Keyes, 1895, Missouri Geol. Surv., vol. 
