278 PALAEONTOLOGY OF ILLINOIS. 



In first publishing a description of the beautiful species forming the type of 

 this genus, we referred it provisionally to McCoy's genus Palasterina, under 

 the subgeneric name Schcenaster. Later comparisons, however, have satisfied 

 us that it cannot properly be retained in that genus; and as it seems to present 

 equally important differences from all the other established genera known to 

 us, we now propose to separate it as a distinct genus, under the name Schce- 

 naster. It is probably most nearly allied to the Silurian genus, Palasterina, 

 but differs in the peculiar oblique, outward, imbricating character of its row of 

 plates on each side of the ambulacral furrows, and the distinct inward imbrica- 

 ting character of the minute, scale-like plates covering the under side of .the 

 disc. There are likewise differences in the arrangements of the plates and 

 pores of the dorsal side of the free arms, as seen in our fig. lb, pi. 19. 



As the disc is not seen in the specimen from which fig. Yof, of the plate just 

 alluded to, was drawn, it presents so different an appearance from fig. Ya of the 

 same plate, showing the upper side of the fossil, that, looking at these figures 

 alone, doubts might arise whether or not they belong to the same type. An 

 examination, however, of the upper side of the same specimen from which Id 

 was drawn, as well as of other fragments, show them to be the same. A frag- 

 ment of the same specimen from which fig. Id was drawn also shows portions 

 of the under side of the disc. 



Another species, apparently of this genus, from the Burlington limestone, 

 with much narrower ambulacral furrows,* shows numerous little short, flattened, 

 spine-like appendages protruding from these furrows, with an outward imbri- 

 cating arrangement or inclination towards the extremities of the rays. There 

 may have been other little spines over the outer surface, in addition to those 

 fringing the margins of the disc, though the specimens retain no traces of them. 



SCH(ENASTER FIMBRIATUS, M. and W. 



PI. 19, Fig. la, lb, 1c, Id. 



Palasterina (Schcenaster) fimbriata, Meek and Worthen, Oct., 1860. Preceed. Acad. 

 Nat. Sci., Philad., p. 449. 



Body regularly pentagonal star-shaped, with the rays pro- 

 duced into rather acutely pointed arms, which are convex 



* We should explain here, that the ambulacral furrow of the enlarged ray, repre- 

 sented by fig. 7 c of plate 19, is proportionally too broad, in consequence of the acci- 

 dental flattening of the specimen, and in part to the adambulacral pieces being 

 represented proportionally too small. These furrows are more nearly natural in fig. Id, 

 but even in that specimen they are proportionally wider than in undistorted examples. 



