Palaeontographical Society Monographs Volume 22, Nos. 94-99

Palaeontographical Society Monographs Volume 22, Nos. 94-99

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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. 1869 edition. Excerpt: has also been found in the Caradoc at Desertcreat, Tyrone (Survey Mus.). Mr. Salter informs me that internal and external casts abound in a sandstone of the Llandovery age in Galway, and that a species much resembling it also occurs in Ayrshire. Spec. C/zar. Shell thick, round, slightly wider than long; valves moderately convex; hinge-line shorter than the width of shell; areas small, fissure in both valves open and large. Exterior surface marked by numerous fine, thread-like, radiating striae, here and there crossed by concentric lines of growth. In the interior of ventral valve a prominent tooth on each side of fissure. The dental plates enclose an elongated muscular depression of about six lines in length by some four in breadth, somewhat elevated and angular at its anterior extremity. The raised margin which surrounds the muscular cavity is continued to within a short distance of the front in the shape of a narrow mesial ridge, while a broad parallel vascular trunk follows on either side the outer margin of the muscular cavity as vell as of the mesial ridge, where, turning outwards and backwards, it encloses wide ovarian spaces. In the interior of the dorsal valve a large wide fissure encloses a concave cavity, longitudinally divided along the middle by a narrow mesial ridge; the brachial processes are very small, while a convex mesial longitudinal ridge separates into two pairs the quadruple impression formed by the adductor or occlusor muscle; the upper or posterior pair are transversely oval, while the anterior pair are obliquely placed, and deeply indented or forked laterally. Length 12, depth 13 lines. 06.2. This is a very distinctive and singularly marked species. Externally it is finely striated, as in O. reversa, but is...
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Product details

  • Paperback | 106 pages
  • 189 x 246 x 6mm | 204g
  • United States
  • English
  • black & white illustrations
  • 1236959515
  • 9781236959515