FOSSIL ASTERIADvE. 



DESCRIPTION 



OF THK 



LIASSIC AND OOLITIC SPECIES. 



Genus— URASTBU, Arjassh, IS35. 



Stellonia, Nardo, 1834. 



UiiASTER, Agassh, pars, 1835. 



AsTEKiAS, Grey, 1841. 



AsTERACANTiiioN, Muller and Troschel, 1840. 



Uraster, Forbes, 1841. 



Fig. 32. 



Rays five, more or less cylindrical, and deeply cleft. The skeleton is composed of small, 

 irregular-shaped ossicula, articulated together 

 in a retiform manner, as seen in the subjoined 

 section of a ray of Uraster ruhens, Lin. 

 (fig. 33) a, represents the long, femur-like, 

 ambulacral ossicula ; b, the small, short, inter- 

 ambulacral ossicles ; and c is the cavity in 

 the ray produced by this arrangement. 



The whole of the upper surface of the disc 

 and rays is studded with blunt or pointed spines, 

 either scattered singly or grouped together in 

 tufts, and, whether single or fasciculate, arranged 



more or less regularly in longitudinal rows (PI. I, fig. 2, a). The integument between the 

 spines is naked, and shows the base of the spines ; in the interspinous portions of the in- 

 tegument are many respiratory pores (PI. I, fig. 3, a, h). Numerous pincers-like pedi- 

 cellariae, supported on soft stems are scattered among the spines or arranged in circles 

 around their bases. 



Section of a ray of Uraster rubens showing the arrange- 

 ment of the calcareous ossicula. 



