378 Dr. T. Wright on new Species of Echinodermata 



careful and minute investigation of the beds exposed in the sec- 

 tion which he has so well described*, added to the discovery of 

 new forms of Radiata and Mollusca in the same, has enriched 

 our knowledge of the Liasic fauna of Gloucestershire. 



Ophioderma Griesbachii, Wright. PI. XIII. fig. 2 a, b. 



Diagnosis. — Body-disc small, upper surface not exposed, under 

 surface irregularly subpentagonal, formed of five pairs of heart- 

 shaped plates ; rays long, slender, and awl-shaped, prolonged 

 beneath into the centre of the body-disc ; inferior surface with 

 median vertebrate-like elements, and lateral scutal plates in 

 the form of oblique pyramidal pieces, which clasp the sides of 

 the rays in an imbricated manner, and support at their ter- 

 minal points short stout spines ; mouth subpentagonal, sur- 

 rounded by ten blunt spinous processes, formed by the deve- 

 lopment of the first lateral scutal plates of the rays, where they 

 join each other around the mouth. 



Diameter of the body-disc /(jths of an inch, length of the rays 

 from the mouth-margin to their apex |^ths of an inch. 



Description. — This beautiful Brittle-star of the Oolitic sea was 

 discovered by our friend the Rev. A. W. Griesbach, of Wollaston, 

 and we owe to his kindness and liberality the series of exquisite 

 specimens before us, by which we have been enabled to complete 

 the description of this new fossil. The body-disc is small, con- 

 sisting of five pairs of heart-shaped plates ; the union between the 

 separate elements of the disc was very intimate, as it is only at 

 one or two points that a suture is exhibited ; so close is the union, 

 that in other specimens the body-disc seems to be formed of a 

 single circular element ; each pair of plates has a heart-shaped 

 form, and the ray corresponding thereto stands out in bold relief 

 from the under surface of the disc. In none of the specimens 

 found is the upper surface of the disc exposed, and we know 

 not with certainty what kind of ornamentation adorned its 

 dorsal surface ; at one part, however, where a portion of one 

 of the plates is weathered, we think we detected with our 

 inch object-glass under the microscope, a series of small imbri- 

 cated scales resting on the rock surface ; the rays are long, 

 slender, and gently tapering ; their under surface, the only one 

 exposed, exhibits, 1st, a central element having an elongated 

 form, which resembles the body of a fish's vertebrse in miniature ; 

 2nd, lateral elements more largely developed, consisting of tri- 

 angular plates of a pyramidal form slightly twis*:ed round, by 

 which arrangement the apices of the pyramids are made to clasp 



* Railway Cuttings at Mickleton Tunnel and Aston Magna, by G. E. 

 Gavey, Quart. Journ. Geol. Soc. February 7, 1853. 



