Stratigraphy and Paleontology of the Alexandrian Series in Illinois and Missouri (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ...ventral valve. The shells are concavo-convex, semi-elliptical in outline, length of different specimens 15 to 20 mm., width about equaling or slightly exceeding the length, greatest at or near the hinge line; the lateral margins almost straight, rounding gradually to the regularly convex anterior margin. Ventral valve rather strongly convex in the median portion, most prominent in the umbonal region, the surface sloping rather steeply, with a concave curvature to the cardinal extremities, and with a gently convex curve to the lateral and anterior margins. Cardinal area narrow, beak low, scarcely projecting over the cardinal margin. Dorsal valve gently and rather uniformly concave, the concavity distinctly less than the convexity of the ventral valve. beak low, not projecting. Surface of both valves marked by very numerous fine radiating striae, some of which are somewhat alternating in size, of which four or five occupy the space of 1 mm., only a few extending to the beak. Occasionally indistinct lines of growth are sometimes present, and in some shells the ventral surface is gently undulating. This species is common in the oolite member of the Edgewood limestone at Louisiana, and near the mouth of Buffalo Creek, in Pike County, Missouri, and south of Hamburg, in Calhoun County, Illinois. For synonomy and description of" this species see page 47 of this paper, under the fossils of the Girardeau limestone. This form is rather rare in the thick layers of gray limestone in the upper part of the Edgewood formation, in Illinois and in corresponding strata near Edgewood and at Louisiana, Missouri. i 1868. Hemipronites subplanus? Meek and Worthen, Ill. Geol. Survey, vol. 3, p. 349. 1868. Hemipronites propinquus. Meek and Worthen, Ill. Geol. Survey, ...