Memoirs of the Museum of Comparative Zoology at Harvard College Volume 31

Memoirs of the Museum of Comparative Zoology at Harvard College Volume 31

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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. 1904 edition. Excerpt: ...coriaceum A. Ag. 1879, Proc. Am. Acad. Vol. XIV, p. 201. Asthenosoma coriaceum A. Ag. 1881, "Challenger " Echinoidea, p. 88. Plate 52. As there is no very detailed figure of the abactinal system of an Asthenosoma, I have given on PI. 52, fig. 1, a figure of the abactinal system and adjoining coronal plates of A. coriacetim from a "Challenger" specimen (fragment from 310 to 315 fathoms, " Challenger" Station 173, off the Fiji islands) of 125 mm. in diameter. The abactinal specimen measured 38 mm. In none of the Echinothurise I have examined are the plates of the abactinal system so greatly subdivided as in A. coriaceum. The ocular plates alone are readily isolated; they are crescent-shaped with truncated horns, the ambulacral system entering deeply into the crescent of the plate. The ocular plates vary considerably in size; the odd anterior ocular, the largest, is nearly twice as large as the smallest ocular, --the right posterior. The oculars and genitals are separated by anal plates with the exception of the madreporic genital, which is connected with the adjoining oculars, and the right posterior one, which has a point of contact with the odd posterior genital. The genitals are triangular, longer than broad, extending in the median line to the third interambulacral plate. The position of the genital opening also varies considerably. In the odd posterior genital it is in a bare space near the anal base of the plate; in the madreporic genital, at the very tip of the genital plate and in the others, in a bare space in the distal part of the plate (PI. 52, fig. 1). All the genital plates are greatly broken up into distinct plates--so much so that it is impracticable to distinguish the original anal plates from...show more

Product details

  • Paperback | 76 pages
  • 189 x 246 x 4mm | 154g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236816870
  • 9781236816870