Author Description

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. 1918 edition. Excerpt:...Union Station, Denison, Texas (604). HORIZON: Weno formation, blue shale, Red River region, occasional; clay ironstone, occasional. LOCALITY: 604, Frisco cut, three-fourths mile north of Union Station, Denison, Texas (type locality); 601, pit of brickyard, one and threefourth miles southeast of Gainesville, Texas. DESCRIPTION: Shell sub-equivalved, moderately inflated, inequilateral, beaks placed back of the middle of the valve. Ventral margin a long, sub-elliptical curve, sharply angulated posteriorly, more rounded anteriorly. Anterior margin long, slightly cenvexed, beaks opposite, approximate; posterior margin shorter than anterior, nearly straight, lacking a prominent incision just posterior to the beaks. Anterior areas crescentic, together forming an elongate biconvex strip, posterior areas forming a strip proportionately shorter but equally wide. These are crossed by plain recurved growth lines. Valves nearly smooth in appearance; ornamentation consists of numerous fine simple radial striaeiform ridges, crossed by growth lines and growth rings. These ridges on reaching the ventral border form a slightly incised, non-crenulate edge. Hinge taxodont, essentially as in Nucida nokonis. This species differs from N. nokonis in its form and ornamentation. The anterior margin is straighter and longer; the posterior margin is straighter and lacks the sharp notch just back of the beaks, having instead a gentle curvature; the posterior "areas" are much more pronounced in side view, and instead of lying flat are elevated at the line of junction of the valves by a posterior projecting carina. The ornamentation at once distinguishes the two species, for in N. nokonis the radial ribs are very pronounced and the concentric growth lines on crossing...