﻿24 FOSSIL ASTEROIDEA. 



broken extremity as compared with the breadth at the base ; there would appear to 

 be every indication that only a small part of the ray is preserved. 



The thickness of the margin at the median interradial line is 13 mm., and 

 at the base of the ray 8*5 mm. The breadth of the ray at the base is about 

 12 mm. 



Locality and Stratigra/phical Position. — The example above described, which has 

 been drawn on PI. IX, fig. 1 a, was obtained from the Upper Chalk in Kent, but 

 unfortunately the exact locality is unknown. It is preserved in the British 

 Museum. A fine fragment preserved in the Museum of Practical Geology, 

 J ermyn Street, was obtained from the Upper Chalk of Bromley. The species has 

 also been found in the Upper Chalk of Sussex. 



History. — 'The type of this species was first described by Forbes under the 

 name of Goniaster (Astrogonium) angustatus, and was afterwards figured by him in 

 Dixon's ' Geology and Fossils of the Tertiary and Cretaceous Formations of 

 Sussex,' London, 1850, pi. xxiii, fig. 10. That illustration does not, however, 

 give a good idea of the facies of the species. 



Genus— PENTAGONASTER, Linck, 1733. 



Pentagonaster, Linck. De Stellis marinis, 1733, p. 20. 



— Schiilze. Betrachtuug der versteinerten Seesterne uad ihrer 



Theile, Warschau u. Dresden, 1760, p. 50. 

 Goniaster (pars), L. Agassiz. Prod. Mou. Eadiaires, Mem. Soc. Sci. Nat. 



Neuchatel, 1835, t. i, p. 191. 

 Astrogonium (pars), Miiller and Troschel. System der Asteriden, 1842, p. 52. 

 Goniodiscus (pars), Miiller and Troschel. Ibid., 1842, p. 57. 

 Hosta (pars), Gray. Ann. and Mag. Nat. Hist., 1840, vol. vi, p. 279. 



Tosia, Gray. Ibid., 1840, vol. vi, p. 281. 



Body depressed and pentagonal in contour, or with the rays slightly produced. 

 Marginal plates smooth or granular, ordinarily few in number. Supero-marginal 

 plates form a broad border to the disk, and, when the ray is produced, are sepa- 

 rated throughout by abactinal plates. Abactinal area covered with rounded or 

 polygonal plates, which may either be smooth or bear co-ordinated granules. 

 Actinal intermediate plates and infero-marginal plates smooth or granulose, devoid 

 of prominent spinelets. 



Much diversity of opinion has existed, unnecessarily it seems to me, as to the 



