Monograph on the Lias Ammonites of the British Islands Volume 1

Monograph on the Lias Ammonites of the British Islands Volume 1

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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. 1886 edition. Excerpt: ...his var. B, and Sowerby's name for var. A (see p. 270). In accordance with this view I have excluded all references to the synonyms of authors, unless I had a figure or a specimen for my guide, to determine the form referred to in the citation; this mode of proceeding has necessarily diminished the list, but makes it more correct for reference. Arietites bisulcatus has a depressed discoidal shell, with a strongly tricarinated siphonal area and subquadrate whorls. The sides are provided with from thirty to forty simple, narrow, slightly-bent ribs, each terminating in a blunt tubercle, near the siphonal border. From the tubercle the rib bends sharply forwards, and disappears at the outer carinae. The area is flat and tricarinated, the median keel a little more prominent than the laterals, and the two sulci, although well marked, are not very deep in the specimens I have examined; the lateral carinte are well defined; the shell is bevelled off from the ridge to the row of tubercles, and presents a series of oblique undulations occasioned by the vanishing of the ribs. The spire is composed of subquadrate whorls; in a specimen, 5-inches in diameter, there are six whorls visible; on the outer whorl are thirty-seven ribs; on the second, thirty; on the third, twenty-nine; on the second, twenty-five; so that in this example the number of ribs increases with the number of the whorls. The aperture is quadrate, rather higher than wide, a little enlarged at the spire, and sinuous above, where it is marked by the central keel, the sulci, and lateral carina-: . (Pl. III and IV.) The septa are symmetrical, foliated on each side, and divided into three lobes, and three saddles formed of unequal parts (Pl. III, figs. 1, 2, 3; Pl. IV, fig. 4). Siphonal...show more

Product details

  • Paperback
  • 189 x 246 x 10mm | 354g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236743628
  • 9781236743626