ASTROPECTEN. 



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Genus— ASTROmC'Tm, ZincL, 1733. 



Stellaria, Nardo, 1834. 

 AsTERiAS, Agassiz, 1835. 



— Forbes, 1841. 

 AsTROPECTEN, Milller und Troschel, 1842. 



Body stellate, flat on both sides, rays elongated. Two rows of large marginal plates at 

 the border. The lower series provided with spine-like scales, which increase in size from 



within outwards, and terminate in long, 

 moveable spines. The dorsal marginal 

 plates are covered with granules, which 

 often become spinous, and sometimes carry 

 spines. The flat upper surface of the body 

 and rays is thickly covered with append- 

 ages, the summits of which are crowned 

 with groups of minute spines. This genus 

 „ . , , is the most abundant in the oolitic Rocks, 



Portion of a ray of Asfropecten poly acanthus, M. and T. J, under 



surface; fi, the upper surface of the ray. the Lias, Inferior Oolitc, Great Oolitc, 



Kelloway Rock, Coral rag, Kimmeridge 

 clay, and Portland beds. All contain species characteristic of each of those divisions of the 

 Jurassic series ; the structural characters of these fossils are so admirably preserved in afl our 

 examples that we have no difficulty in referring them to the existing genus Astroijecte7i. 



A. — Species from the Lias. 



AsTROPECTEN HastingiyE, Forhes. PI. VI, fig. 3 a, b, fig. 4 a, b. 



AsTROPECTEN Hastingi.^:, Forbes. Memoirs of the Geological Survey of Great BriUiiu, 



vol. ii, part 2, p. 4/8, 1848. 

 — Forbes. Ibid., Brit. Organic Remains, decade 1st, pi. ii, 

 fig- 1. 



— — Wright. British Association Reports, vol. for IS.76, p. 402. 



Rays five, short, acute, lanceolate, sides straight, intermediate angles obtuse ; marginal 

 plates quadrate, subequal ; surface of the disc, on the upper and under sides, covered with 

 small, tetragonal ossicles, arranged in a tesselated order. 



Dimensions. — Diameter of the body from ray point to ray point, nearly tAvo inches ; 

 diameter of the disc, one third of the whole. 



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