KEVISION OF PALEOZOIC STELLEKOIDEA. 151 



largely dependent upon it for our knowledge of the generic charac- 

 ters " (p. 350). 



Emended description. Disk large, with moderately developed inter- 

 brachial arches. Rays five, short, and tapering more or less rapidly. 

 U R about twice as great as r." 



Abactinal area of rays distally with one medial column of large, 

 thick, and subquadrangular radial plates, on each side of which are 

 similar columns of supramarginal and inframarginal pieces. In this 

 region the columns adjoin and the ossicles are crowded, but 

 proximally between the radial and supramarginal and between the 

 latter and the inframarginal columns (ambital areas) are inserted 

 numerous accessory smaller plates. The latter are most numerous 

 in the ambital areas and at the base of the rays. The ossicles are 

 packed into a tessellate pavement. In the center of the disk there 

 seems to be a prominent central disk piece and at the bases of the 

 rays there is a somewhat disconnected ring of ten most prominent 

 plates, the five basal pieces of the radial and five interradial that 

 give rise to the ten supramarginal columns. Inside of this ring there 

 are probably numerous, very small pieces with no definite arrange- 

 ment. A number of the proximal plates of both the radial and 

 supramarginal columns may be separated from one another by small 

 accessory pieces. 



Madreporite abactinal. 



Inframarginal plates bounding the entire outer edge and common to 

 both sides of the animal. These plates are, however, small (smaller 

 than the adambulacrals) and bear tufts of small spines. 



Adambulacrals subquadrangular, and closely adjoining, each plate 

 bearing on its outer lateral edge a tuft of three spines. Oral armature 

 consists of five pairs of triangular adambulacral plates which have 

 slender spines on the inner edges. 



Interbrachial areas extending to near the distal ends of rays and 

 occupied by numerous "isolated rounded or subangular [accessory 

 interbrachial] plates bearing [single] small spines." 



Ambulacrals slightly alternating and about as numerous as the 

 adambulacrals. Each plate has an L-shaped ridge, posteriorly 

 directed. The podial openings are on the sutures between the 

 ambulacrals and adambulacrals. 



Genoholotype. Uraster prims&vus Forbes. The above diagnosis is, 

 however, based largely upon Palasterina bonneyi Gregory. Dr. 

 Bather sent the writer a number of wax squeezes of the genoholo- 

 type, and while the parts preserved are clear and sharp, yet the speci- 

 mens are not complete enough to work out the generic characters. 

 Therefore, for the present, P. bonneyi is taken as the genoholotype. 



Distribution. Ludlow shales (Upper Siluric) of Great Britain. 



