. Annual report. New York State Museum; Science; Science. SOME NEW DEVONIC FOSSILS 267 to margin and number from 16 or less in small individuals to 26 in the largest shells seen. In full growth of the shell the median rib becomes more pronounced than the rest on the anterior margin and thus makes a low median angle at this margin. Extremely fine concentric lines are visible under favorable preservation. The cardinal area is narrow and only in rare instances are spines re- tained or developed at the cardinal extremities. On the interior the brachial valve has a small erect V-shaped cardinal pro
. Annual report. New York State Museum; Science; Science. SOME NEW DEVONIC FOSSILS 267 to margin and number from 16 or less in small individuals to 26 in the largest shells seen. In full growth of the shell the median rib becomes more pronounced than the rest on the anterior margin and thus makes a low median angle at this margin. Extremely fine concentric lines are visible under favorable preservation. The cardinal area is narrow and only in rare instances are spines re- tained or developed at the cardinal extremities. On the interior the brachial valve has a small erect V-shaped cardinal process and short thin outer socket walls. On each of the simple coarse ribs which correspond to the furrows of the exterior is a single row of sharp pustules the median row being the most depressed, and the two adjoining the most prominent. No trace of reniform or other lateral depressions is evident. In all such small and coarse ribbed species represented by C. billings i, C. laticosta Hall and '%(Jr. Chonetes billingsi C. mucronatus Hall, there is a natural similarity of expression extending even to the interior characters of the brachial valve, but the distinctive differences of C. billingsi consist in its gib- bosity, angulated front margin at maturity, stronger, coarser and more uniformly simple ribs. In respect to these characters in all the shells they are the most pronounced in that before us and be- come progressively decreased in the upward range of the group, so that it serves the purposes not only of paleontologic but also of geographic distinction to recognize distinctively this early manifes- tation of features which are less pronounced in C. laticosta of the Onondaga limestone and still further diminished in C. mucronatus of the Marcellus and Hamilton. Dimensions. A full sized example has a width on the hinge of 13 mm and a length of 11 mm. From this the size ranges downward to a length of 2 mm. Lower Devonic. Grande Greve, P. Q. Middle Devonic. Gaspe Basin, P.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectscience, bookyear1902
