Illustrations and Descriptions of New, Unfigured, or Imperfectly Known Shells, Chiefly American, in the U.S. National Museum

Illustrations and Descriptions of New, Unfigured, or Imperfectly Known Shells, Chiefly American, in the U.S. National Museum

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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. 1902 edition. Excerpt: ...of the whorls are so or not, indicating the derivation of_ the group from a cancellated, or, at least, a sculptured ancestral type. The typical Trophons are chiefly austral and have a rather characteristic type of form and sculpture. The boreal forms show more variety and have developed several types among themselves, all different from the antarctic group, and which I therefore separate as a genus, Boreatrnpkrm (Fischer, 1884). This genus, again, is divisible into several sections characterized by their sculpture. The typical Boreotrq/aon has lamellar varices, the spiral sculpture is absent or feeble, and the operculum is elongated and narrow with the nucleus apical, and no purpuroid markings on the inner face. The section T rop/amwpsis (B., D., and D., 1882) has spiral sculpture quite emphatic, and some times the varices are obsolete. The operculum is short and wide with an apical nucleus, but with purpuroid markings on the inner face. In each group a transition toward the other section may be observed in some species. ' Both agree in dentition and station. In the majority of species there is occasionally developed a carina at the shoulder over which the varices are elevated into spines or elevated scales.. There are, however, species which always have an angle or varical spine at the shoulder. The development of the varices is different in different individuals of the same species, as in Murex; specimens from a fine sandy or soft bottom will frequently have remarkably broad, thin, expanded varices; while those from an unfavorable situs, as a gravelly bottom, may have the varices degenerated to mere lines hardly raised above the surface except at the shoulder. These differences, though systematically not important, affect the...show more

Product details

  • Paperback | 32 pages
  • 189 x 246 x 2mm | 77g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236843568
  • 9781236843562