OPHIODERMA. 147 



Ophioderma Gaveti, WriffJit, 1853 ; PI. XV, fig. 1, a, b, c, d, 2, 3; PI. XVII, fig. 1, a, h. 



Ophiodebma Gaveyi, Wright. Annate and Mag. of Nat. Hist. 2nd series, vol. xiii, 

 p. 183, pi. xiii, fig. 1, 1854. 



— — Forbes, in Morris's Catalogue of Brit. Fossils, 2nd ed., 



p. viii, 1854. 



— — Wright. Brit. Association "Report for 1856, p. 402, 1857. 



Disk large, flat, circular ; radial plates large, the pairs closely approximated, and 

 separated from the adjoining radial plates by an interval ; arms long, slender, tapering 

 gradually ; dorsal and ventral plates narrow, the dorsal with a central carina ; lateral plates 

 support short, stiff, pectinated spines ; base wide, oral opening small, surrounded by five 

 pairs of very prominent tooth-like processes. 



Dimensions. — Diameter of the disk, one inch and four tenths ; diameter of the rays at 

 their junction with the body, one fourth of an inch ; length of the rays, four times the 

 diameter of the disk. 



Description. — This Ophiura is found as yet only in one horizon of the Middle Lias, 

 and many fine specimens have been discovered in the original locality near Chipping 

 Camden ; the one showing the upper surface (PI. XV) is in my cabinet, that showing the 

 base belongs to the Museum of the Worcestershire Natural History Society, and I am 

 indebted to my friend Sir Charles Hastings, the President, for his kindness in allowing 

 this fine specimen to be figured in my work. 



The disk is large, flat, and circular, slightly inclining to a pentagonal form ; it is 

 composed of ten thin, triangular, radial plates, arranged in pairs, each pair forming a 

 heart-shaped shield, with an elevated central carina, formed by the rudimental dorsal 

 plates of the rays covering the prominent vertebral osselets ; each pair appear to have 

 been firmly articulated together along the median line, and free from the adjoining 

 pairs at their margins ; their surface is smooth, and at the apex of the plates ten 

 elevated eminences indicate the bifurcated terminations of the radial carinas (PI. XV, 

 fig. 2). The rays are long, slender, and taper gently; the dorsal plates are small and 

 hexagonal ; they are nearly all absent, leaving the osselets thereby exposed (PI. XV, 

 fig. 1 b, \,c). This defect gives a peculiar character to the dorsal surface of the ray, 

 which might be mistaken for' a kind of ornamentation ; the lateral plates are rounded 

 and closely imbricated, and their free border is toothed with five or six pectinated 

 processes, which in the living state supported spines XPl. XV, fig. 1, c, fig. 2, and fig. 3) ; 

 the remains of these are sometimes seen attached to their supports ; the lateral plates 

 clasp the rays firmly and securely, and overlap the dorsal and ventral plates, the latter 



20 



