74 FOSSIL ASTBROIDEA. 



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. Bach 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. PL XXII, figs. 1, 1 a, lb,2,2a, 3 a, 3 b, 



3Q 7 Q 

 tj O Uj O i 



OBEASTEE OBTUSUS, Forbes, 1848. Mein. Geol. Surv. Gt. Brit., vol. ii, p. 468. 



Forbes, 1850. In Dixon's Geology and Fossils of the Tertiary 

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

 pi. xxi, fig. 12. 

 Dujardin et Hupc, 1862. Hist, Nat, Zooph. Echin. (Suites a 



Buffon), p. 389. 



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

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



