Pal Ozoic Fossils (Volume 2, PT. 1)

This historic book may have numerous typos, missing text, images, or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1874. Not illustrated. Excerpt: ... Fig. 7. Fig. l.--Choneles Canadensis. A specimen of the long form. Specimens much broader and shorter proportionally occur. The upper figure shows the area, that of the ventral valve uppermost. Description.--Shell semi-circular or semi-elliptical, the proportional length and width variable. Ventral valve gently convex, in general most elevated at about one-third the length from the beak; the cardinal angles flattened or slightly concave; umbo broadly depressed, convex; beak scarcely distinguishable from the cardinal edge. The area is rather large, being about a line high at the beak; nearly flat or very slightly concave, nearly smooth, no traces of crenulations; inclining backwards at an angle of about 45 with the plane of the lateral margin. The foramen is triangular, its width at the base nearly twice its height, extending nearly to the beak. Dorsal valve gently concave, corresponding to the ventral valve, in its curvature, so as to leave only a thin space between them. The area is about one-third or one-half the size of that of the ventral valve, and forms nearly a right angle with the plane of the lateral margin. The surface is covered with very fine, obscure radiating striae, from ten to fifteen in the width of two lines. Some specimens, also, exhibit a number of concentric ridges or undulations of growth. Many show shallow, concave furrows from half a line to one line wide, which radiate from near the beak to the margin. These are most distinctly seen in specimens from which the shell is either wholly or partially removed. In such cases these furrows are either straight or slightly curved, the convex side of the curve being outwards, towards the sides. When the shell is a little worn fine closely arranged punctures may be 6cen between the st...