100 



FOSSIL OOLITIC ASTERIAD^E. 



The wide ambulacral avenues are composed of two rows of long, compressed, femur- 

 shaped bones, through which four series of tentacular or sucking-feet protrude (PL I, fig, 2,(5). 

 The vent is small and subcentral. The madreporiform body is single. The Urasters are 

 found in all seas, but they prevail most in those of the Arctic and Atlantic regions ; whilst 

 in warm climates they are limited in numbers. Their presence, therefore, in any rock 

 affords imperfect evidence of the climatal conditions under which it was deposited. All the 

 oolitic species have hitherto been found in the Lias. 



A. — Species from the Lias. 

 UiiASTER Gaveyi, Forbcs. PI. T, fig. 1, a, h. 



UnASTEii Gaveyi, Forbes. British Organic Remains, Memoirs of tlie Geological 

 Survey, decade iii, plate ii, 1850. 



— — Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 90, 18.54. 



— — IJ^riyht. Monograph of Brit. Oolitic Echinodermata, p. 428, 1855. 



Rays five, moderately lanceolate ; ambulacral areas wide and well exposed ; ambu- 

 lacral ossicles long, arcuate, and bi-carinate ; sides and upper surface of the rays, closely 

 covered, with short, tapering, thorn-like spines ; the proportionate diameters of the disc to 

 the rays is as one to six. 



Dimensions. — Diameter of the disc, one inch and three twelfths ; maximum breadth of 

 a ray, eight twelfths of an inch ; maximum breadth of an ambulacrum, five twelfths of an 

 inch ; length of a ray from the angle of junction with the disc, three inches and a half ; 

 length of an ambulacrum from its origin at the mouth, four inches. 



Description. — The wonderful specimen figured in Plate I was obtained from the 

 Middle Lias at Chipping Campden, in the Zone of Ammonites capricornus ; the four rays 

 which remain exhibit the anatomy of the skeleton in great perfection and disclose the close 

 affinities it has with TJraster ruhcns, Lin., of our present seas, showing that this type of 

 animal structure, at least, has undergone little modification during the inconceivable 

 period of time which has elapsed since the Lias formation was deposited. This Star-fish 

 lies on its upper surface, in a slab of Lias, among which are strewed in great abundance 

 Ammonites capricornus, Schloth., Unicarditm, cardiodes, Phil., Cardium truncatum, Phil., 

 Cypricardia cucullata, Goldf., and separate ossicles of Dentacrinus robustus, Wr. The 

 nnder surface (fig. \,a) is fully exposed, and small portions of the upper surface are likewise 

 seen, which partly display the general character of the structure and clothing of the dorsal 

 integument ; the upper surface of the rays appears to have been covered with short, stout, 

 tapering spines, set very closely together on that portion of the integument exposed on the 



