Palaeozoic Fossils

Palaeozoic Fossils

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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. 1865 edition. Excerpt: ...preserved in the specimens observed. Area wide, flat, sloping a little backwards. Dorsal valve moderately convex, with an obscure fold in the front half. Surface with very fine radiating striee, six to nine in the width of one line. Width from 5 to 6 lines; length varying from two-thirds to three fourths the width. The sides in the upper half are sometimes straight and parallel, and sometimes rounded. Anterior angles rounded. The front margin is usually straight, or a little concave, in the middle. Locality and Formatz'on.--Stanbridge, range 6, lot 20; Quebec group. Collector.--T. C. Weston. Fig. 293.--Orlhis./Irmanria. a, ventral valve of a wide variety; b, ventral vnlve ofa narrower form, showing a cast of the interior of the beak and umbo; c, dorsal valve. Descrz'ption.--Shell of medium size, varying in width; hinge line straight; cardinal angles 90, or often a little less; sides straight, and either parallel or a little converging from the hinge line forward for onefourth or one-half the length; anterior angles and front margin rounded. Ventral valve pyramidal, varying in height, the beak usually the most elevated point, thence with a convex or straight slope to the anterior angles and margin, the slope to the cardinal angles either flat or gently concave. Dorsal valve depressed convex, concave towards the cardinal angles; beak scarcely elevated above the hinge line. The area of the ventral valve is rather large, sometimes three lines in height, often less, very variable in this respect, either at right angles to the plane of the margn, or inclined thereto sometimes as low as 45. Foramen moderate, apparently open. In the interior the dental plates seem to form an imperfect triangular chamber, thus dilfering somewhat from the more

Product details

  • Paperback | 192 pages
  • 189 x 246 x 10mm | 354g
  • United States
  • English
  • black & white illustrations
  • 1236889363
  • 9781236889362