Bulletin; Bureau of Economic Geology Publications Volume 56

Bulletin; Bureau of Economic Geology Publications Volume 56

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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...show more

Product details

  • Paperback | 84 pages
  • 189 x 246 x 4mm | 168g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236613260
  • 9781236613264