74 FOSSIL ASTEROIDEA. 



vaguely as Upper Chalk, Sussex. The specimen is somewhat imperfect, consisting 

 only of the dorsal view of three arms and a portion of the disc. 



Description . — The disc appears to have been covered on its dorsal surface by a 

 large number of small, rounded, closely-fitting plates. Mostly they are subequal 

 in size and have an approximate diameter of 2 mm. An uncertain number of 

 even smaller granule-like plates exist scattered between these. 



Both radialia and adradialia extend into the base of the arms, but only as far 

 as the third supero-marginal plate, counting from the median interradial line. 

 The arms themselves are short and high. The height of the specimen in the 

 interradius is 9*2 mm. From this point the height gradually diminishes to the 

 extremity of the ray, where it is 5 mm. 



The supero -marginalia are about twelve in number. They form a broad 

 margin to the disc and rays. Each supero-marginal plate is high, and is very 

 convex dorsally. Hence every plate is very distinct. The six proximal supero- 

 marginals diminish only slightly in size distalward along the ray. The next six, 

 however, diminish much more rapidly. The supero-marginal nearest the inter- 

 radius has the following measurements: height, 5*75 mm.; breadth, 4*5 mm.; 

 length, 3 mm. 



The ocular plate has broken away, and there is no trace of a madreporite. 



The infero-marginalia alternate with the supero-marginal series. They are 

 not so high and much squarer in appearance. They decrease in size much more 

 rapidly than the upper series (see PI. XXI, fig. 2 a). The infero-marginal plates, 

 nearest the interradius, measure 4*5 mm. high and 3*2 mm. in length. Any orna- 

 ment that may have existed has disappeared from all parts. 



Locality and Stratigraphical Position. — Upper Chalk, Sussex. 



4. Pentagonastee obtusus, Forbes, sp. PI. XXII, figs. 1, 1 a, 1 b, 2, 2 a, 3 a, 3 b, 



3 c, 3 d, 3 e, 3/, 3 g. 



Oreaster obtusus, Forbes, 1848. Mem. G-eol. Surv. Gt. Brit., vol. ii, p. 468. 



_ — Forbes, 185U. In Dixon's Geology and Fossils of the Tertiary 



and Cretaceous Formations of Sussex, London, p. 330, 

 pi. xxi, fig. 12. 

 — Bujardin et Hupe, 1862. Hist. Nat. Zooph. Echin. (Suites a 

 Buff on), p. 389. 

 — — Forbes, 1878. In Dixon's Geology of Sussex (new edition, 



Jones), pi. xxi, fig. 12, pp. 364, 370. 



