Bulletin Volume 542-546

Bulletin Volume 542-546

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ...The anterior end below the beaks is slightly concave, but the lunule is at best ill defined and there is no distinguishable escutcheon. Just back of the beaks, however, the shell is excavated along the margin into linear grooves, one on either valve, for an external ligament. The surface is generally smooth but is sometimes marked by a few faint concentric strise. Many specimens have a few larger and deeper incremental striae, especially toward the margin. On the interior there are the usual large anterior and posterior adductors, the latter situated near the cardinal line and close to the posterior margin. Slightly above and anterior to the posterior scar is another somewhat smaller scar which in some specimens is clearly duplicate, one portion being more deeply impressed than the rest. In a few individuals a fourth scar, rather large, but not deeply impressed, can be seen between the beaks and the anterior adductor. The dentition is fairly well shown by the specimens, though certain details remain still in doubt. Apparently the posterior teeth extend quite to the beak, gradually diminishing in size until the final ones are very diminutive. Under the beak the posterior teeth meet the anterior ones, which do not show a corresponding diminution in size and are therefore much larger than those which abut against them. I think there can be no reasonable doubt that a chondrophore is present, but, unlike the chondrophore of living nuculoids it does not extend to the beaks, thus interrupting the dentition, but is interior to the row of teeth which surrounds the margin, and at a somewhat lower level. I can not he absolutely certain that this difference, which has been observed also in Leda beUistriata, really exists, but such are the...show more

Product details

  • Paperback | 506 pages
  • 189 x 246 x 26mm | 894g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236921771
  • 9781236921772