CONTRIBUTIONS TO PALEONTOLOGY. 333 



a double series of alternating subquadrate ambulacral ossicles, and a 

 series of curved adambulacral plates bordering the grooves, and 

 forming the margin of the ray : the outer ends overlap the edge of 

 the next plate in advance. Oral plates ten, arranged in pairs, form- 

 ing the terminal plates of the adambulacral ranges. Pores large, 

 arranged in two rows in each ray ; penetrating the ray at the junc- 

 tion of the ambulacral and adambulacral plates in such a manner 

 that four different plates border each perforation. Adambulacral 

 and disc-plates bearing spines. Dorsal surface unknown. 



The genus is allied to Protaster, Forbes, but differs in the structure 

 and arrangement of the component parts of the ray, and in the manner 

 in which the pores penetrate the plates ; it also differs in the form of the 

 disc, which is not circular, but extends for some distance along the rays, 

 forming acute alations on their margins. The plates of the disc are 

 polygonal, united by their lateral faces, and not squamose as in Pro- 

 taster. The Genus Palasterina has " the arms a little produced " 

 beyond the disc, while in this one they are much produced. The 

 structure of the ray is in general characters similar in the two genera, 

 but in Palasterina the adambulacral plates are large and quadrangular, 

 while in this they are subsquamiform, spiniferous subimbricating. 



EUGASTER LOGANI, N. S. 

 PLATE IX, FIGS. 7 and 8. 



Body stellate, with a small disc and long attenuate flexuose rays. Disc 

 composed of numerous small polygonal plates with radiated surfaces ; 

 the diameter, measured from the sinus to its extension on the oppo- 

 site ray, is about half as great as the length of the ray measured 

 from the centre of the disc. Rays, as seen from the ventral side, 

 narrow, attenuate, with the ambulacral plates curving, and near the 

 base of the rays a little wider than long, and towards the extrem- 

 ities longer than wide, with a strong elevated transverse ridge. 

 There are about eight pairs of plates enclosed within the limits of 

 the disc. Pores penetrating the interstices near the outer extremi- 

 ties of the plates, while near the inner end there is a depression or 

 pit resembling a partially excavated pore. The adambulacral plates 

 as seen from below are extremely narrow and very convex on their 

 outer surfaces, forming the margins of the ray. Oral plates in pairs, 

 narrow and elongate. 



