INVERTEBRATES. 277 



ASTEROIDEA. 



Genus SCHCENASTER, M. and W. 



(ffprotvoc, a rope; acrrTjp, a star.) 



gynon. — Schcenaster (subgenus Palasterina) , Meek and Worthest, Oct., 18-60. Proceed. 

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



Animal consisting of a flattened pentagonal disc, with the 

 angles more or less produced in the form of rays or arms, and 

 the margins between the rays concave in outline, and fringed 

 with short, flattened, spine-like appendages, which are also con- 

 tinued part of the way out along the lateral margins of the rays. 

 Upper side of rays composed of a number of alternating solid 

 plates, with the dorsal pores passing between them, while the 

 angles between the rays are filled with similar plates, forming 

 the upper side of the disc. Under side of disc composed of 

 numerous small plates, very distinctly imbricating inwards 

 and laterally towards the ambulacra. Ambulacral furrows (in 

 the typical species) wide, deep, with on each side, a single row 

 of comparatively stout, squarish or oblong adambulacral pieces, 

 having an obliquely-outward, imbricating arrangement, so as 

 to present somewhat the appearance of a twisted cord, as seen 

 from below; farther out, these become the marginal pieces of 

 the free rays. There is, however, no regular row of marginal 

 pieces to the disc between the rays. Oral pieces ten, anchy- 

 losed? in pairs, so as to look like five pieces merely emarginate 

 at the outer and inner ends. (Other characters unknown.) 



Of course it is not possible to give a systematic diagnosis of a genus like this, 

 of which only imperfect fossil species are known. All that can he done, in 

 cases of this kind, is to give such of the more prominent characters as happen 

 to be visible in the particular specimens accessible; while we cannot always be 

 sure, until better specimens are obtained, and other species known, whether 

 some of the characters given may not be merely specific, or in other cases of 

 more than generic importance. At the same time, we have to regret our ina- 

 bility to give any information in regard to some of the more delicate parts that 

 would be the first to claim the attention of the zoologist in describing existing 

 star-fishes. 



