ASTROPECTEN. 



113 



6Vw?/,s— ASTROPECTEN, LincL, 1733. 



Stellakia, Nardo, 1834. 

 ASTEIUAS, Agassiz, 1835. 

 — Forbes, 1841. 

 AsTROPECTEN. Muller and 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 granul(!s, 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, 

 the Lias, Inferior Oolite, Great Oolite, 

 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 all our 

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



Portion of a ray of Astropecten polyacanthus, ^i. and T. A, under 

 surface; R, the upper surface of the my. 



A. — Species from the Lias. 



Astropecten HASTiNGiyE, Forbes. PI. VI, fig. 3 a, h, fig. 4 a, h. 



AsTROPECTKN Hastingi.e, Forbcs. Memoirs of the Geological Survey of Great Britain, 



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 1856, p. 402. 



Rays five, short, acute, lanceolate, sides straight, intermediate angles obtuse ; mai-ginal 

 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 two inches ; 

 diameter of the disc, one third of the whole. 



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