PALEONTOLOGIC CONTRIBUTIONS 3 I 



and supramarginal ossicles are furnished with thick, short inarticu- 

 late spines. 



Madreporite small, depressed, inside and between two marginal 

 ossicles, marked by indistinctly concentric ridges. 



The actinal area shows broad, ambulacral grooves. The ambu- 

 lacral plates are opposite or but very slightly alternate, subquad- 

 rangular, with a high transverse carina. The podial openings are 

 large. The adambulacral plates equal in number the ambulacral 

 plates; are small; rectangular, or pentagonal, where they adjoin the 



Fig. ii Clarkeaster perspinosus nov. 

 Abactinal disk area and base of arm of cotype 

 (figured pi. 7, fig. 1). (x 2^/2) 



suture of two inframarginal plates. The latter form the most con- 

 spicuous column, are large, rounded quadrangular to oval in out- 

 line, about one of them corresponding to two adambulacral plates. 

 They bear on their outer edge long spines. The ossicles of the oral 

 armature belong to the adambulacral column, are small and obtusely 

 bent so as to form a Y-shaped piece. The interbrachial area is 

 occupied by one large quadratic axillary interbrachial which bears a 

 long central spine. Also the first two inframarginals have large 

 central spines. 



Measurements. Length of ray (R=t,2 mm), radius of disk 

 (r=6 mm), basal width of ray (outside of disk) =5 mm. 



Horizon and locality. Chemung beds, Avoca, Steuben county, 

 N. Y. 



