32 ECIIINODERMS OF THE LONDON CLAY. 



The specimen was procured by the Earl of Enniskillen from the London Clay of 

 Sheppey. I have seen other fragments of the same species. 



Order.— OPIIIURIDEA. 



The Brittle-stars have orbicular or pentagonal bodies, covered above with a skin, which 

 is either naked, squamose, or spinous. Below they liave a central niontli, from which five 

 long, simple, flexible arms, protected by plates and spines, radiate far beyond the disk. 

 At the base of each ray there are two brachial [)lates studding the dorsal surface ; they 

 have no vent. The genital pores open below. Their arms are furnished with cirri. 



Ophiura, Lamarck. 



In the Brittle-stars of this genus the dorsal snrface of the body is covered with smooth 

 scales or plates. The interbrachial shields at the bases of the arms are conspicuous, and 

 there is a fringe of minute spinules on the margins of the small plates above them imme- 

 diately appressed on tlic arm-bases ; these latter are inserted into the disk. The inferior 

 intermediate plates are hollowed out at their sides, and of conspicuous dimensions. The 

 mouth is bordered by projecting ossicles, edged by a single row of minute obtuse papilla-. 

 The side plates of the rays bear appressed spines. 



I. QpniuRA WflfHERELLi. Plate IV, fig. 7. 



Opuiur.\, sp. WelhereU, Geol. Proc, i, p. -117. 

 — Morris, Cat. Br. Fos., p. 55. 



Some years ago ]\Ir. Wetherell put on record an Eocene OijJiiura from near Ilampstead, 

 and has since found at llighgate, in concretionary masses, numbers of small Ophiune all of 

 one species. They have orbicular bodies covered above by rather large plates, arranged 

 more or less concentrically, aiul by large triangular, sub-parallel, brachial shields. Traces 

 of the small clasping scales bearing a comb of spinules, may be seen in one example. The 

 under side exhibits clear traces of the peculiar arrangements of the genus to which it 

 belongs. ^Phe arms are about three times as long as the diameter of the disk, and are 

 gently tapering. The central scales of their upper surfaces change ra])idly from broadly 

 (juadrangular to a sub-triangular shape, and eventually become partially overlapjied by the 

 large lateral scales ; each of the latter bears four or five tapering, rather short spines. On 

 the under side of the ray the lateral scales meet and join nearly to their extremities, where 

 a small triangular central scale is interposed. 



