OPHIODERMA. 



149 



Descrijjtion. — This Ophiura resembles Ophioderma Gavei/i, Wr,, in the general 

 structure of the disk and rays ; the disk, however, is proportionately smaller. The 

 radial plates are closely approximated, and between each pair there is a smooth depressed 

 space ; the margin of the disk appears to have been membranous, and extended like 

 a web between the base of the rays (fig. \, a). In the centre of the disk the ten 

 osselets, arranged in pairs, forming part of the buccal framework, are seen projecting 

 upwards (fig. 1, a). 



The long and slender rays taper gently to their apex ; the dorsal plates are narrow, 

 and form a well-marked carina on the middle of the rays. The lateral plates are large, 

 rounded at their free margin, and closely imbricated ; there are some obscure indications 

 of small dentations on their outer border for the support of spines (fig. \, b). None 

 of the ventral plates are exposed in the only specimen of this species I have seen. 



Affinities and Differences. — This species, in its general form, proportions, and structure, 

 resembles OpUoderma Gaveyi, Wr. ; it is distinguished from that form chiefly in having 

 a much narrower disk and a stronger carina on the dorsal surface of the rays. The 

 plates of the rays are so imperfectly preserved that their characters cannot be accurately 

 determined, and therefore a comparison with those of 0. Gaveyi is impossible. It is 

 always prudent to write cautiously about supposed new forms of which we have only 

 a solitary example to examine, for a series of specimens, were they forthcoming, might 

 show that characters supposed to be specific were only varietal ; it is with much hesi- 

 tation, therefore, that I have separated this Ophiura from the preceding on such feeble 

 characters as a narrower disk, and more largely carinated rays. 



Locality and StratigrapUcal Position. — This Ophiura was collected from the grey 

 micaceous sandstone of the Marlstone at Staithes, where it is very rare ; it appears to be 

 the form which was figured by Young and Bird in plate v, fig. 5, in their work on the 

 ' Geological Survey of the Yorkshire Coast/ of which they say — " This is a handsome 

 Star-fish, having five long and bending arms, not unlike some of a smaller size found 

 recently on our shores. It particularly resembles Asterias splicerulata, or rather we may 

 venture to pronounce it the same, as it shows the five small beads encircling the mouth. 

 Two of this species are in the Whitby Museum, both in clay-ironstone, occurring in the 

 Alum Shale."^ 



The specimen I have figured belongs to the cabinet of my kind friend, John Leckenby, 

 Esq., F.G.S., who has liberally contributed it with his other rare fossils to this work. 



1 ' Geological Survey of the Yorkshire Coast,' p. 210. 



