,834. PROCEEDINGS OF THE NATIONAL MUSEUM. 263 



Odontaster. The large, median, sharp, recurved spine or "keel" of the 

 jaw is the same in both, and the same is true of the general structure 

 of the skeleton. But Odontaster is much more spinose, both above and 

 below, than any of Sladen's species. The latter have more evidently 

 paxilliform plates on the actinal surface, bearing small spinules or 

 papilliform granules, wliile in the type of Odontaster all the ventral 

 jjlates are densely covered with long, robust, erect spines, nearly equal 

 in length. 



ODONTASTER HISPIDUS, V e r r i 1 1 . 

 Odontaster hispidns, Vekkill, oj). cit., j). 402, 1880. 



This form is regularly stellate, with a rather broad, flat disk and 

 tapering, subacute rays, which are usually 5, but sometimes 6. The 

 dorsal surface of the disk and rays is covered with spinulated para- 

 paxilliB; over most ot the surface these have a rather high, round, cen- 

 tral column, (;onvex at summit, and covered with a dense radiating 

 group of long, slender, sharp spinules, often 20 to 26 on each; the 

 marginal spinules are smaller and mostly divergent. Toward the mar- 

 gins of the interradial areas and rays the central column of the 

 plates becomes gradually smaller and shorter, becoming verruciform 

 and quite small on the outer plates, which are closely crowded and 

 without intervening papular pores. 



The papuliB, in specimens 20 to 30 ram. in diameter, are arranged in a 

 broad ovate group at the base of each ray, and in a disconnected cen- 

 tral group on the disk, but in large specimens the central group becomes 

 connected with the others by a narrow median band; the papuhii do 

 not extend quite to the end of the rays in the largest examples, but 

 reach to about the distal third. The madreporic plate is of medium 

 size, with fine gyri, and is surrounded by a ring of about G paxilhe. 



The marginal plates are all convex, with deep rounded sutures, in 

 both directions; the upper ones rest largely on the dorsal side. There 

 is an odd interradial marginal plate in each series, very similar to 

 the others, but a trifle more wedge-shaped. There are usually 17 to 

 19 plates in each series, in the larger specimens; they are opposite each 

 other. The apical plate is small and pear-shaped. 



The upper marginal plates are densely covered with small, slender 

 spinules, like those of the dorsal paxilhe, and the marginal ones are 

 smaller and form narrow fascioles. 



The inferior marginal plates are densely covered with similar spines, 

 which are a little more acute, but they have very slender spinules along 

 the sutures, forming imperfect fascioles. The actinal plates are numer- 

 ous, thick, rather squarish, but with rounded angles and a convex 

 surface, with pits where the spines are removed ; they are arranged in 

 rows parallel to the furrows, except close to the margin, where they 

 become small, irregular, and crowded; those in the first row are longer 

 radially than the adambulacral plates, so that they are fewer than the 



