30 NEW YORK. STATE MUSEUM 



large plates with long spines and five intercalated smaller plates. 

 In Mesopalaeaster there is a first ring of seven pieces and a second 

 of fourteen pieces, outside of which the ring of proximal radials 

 and supramarginals is seen as in Clarkeaster. In the rays the main 

 difference rests in the intercalation of the pairs of accessory plates 

 between the radial plates. There are two interbrachial marginals 

 in each interbrachial area, while Mesopalaeaster "has but one. The 

 actinal side is as in Mesopalaeaster. 



Genoholotype. C. perspinosus nov. 



Remarks. Of the two species belonging to Clarkeaster, namely, 

 C. perspinosus and C . c 1 a r k i , the latter shows the more 

 primitive characters (see under C. perspinosus). Both 

 species representing the genus appear as a later development of the 

 Mesopalaeasterinae Schuchert. In the extreme development of the 

 spines a gerontic feature of this race may possibly be seen. They 

 certainly surpass in this feature any of our Paleozoic starfishes. 



Clarkeaster perspinosus nov. 

 Plate -5, figures 5 and 6; plate 6, figure i; plate 7, figures I and 2 



Description. Rays long, slender, tapering regularly proximally 

 and narrow, whiplike distally. Disk comparatively large. Inter- 

 brachial areas distinct. 



The abactinal side of the disk is most strikingly marked by a ring 

 of ten plates, five of which, the basal plates of the radial columns, 

 are of very large size and produced into large thick spines that 

 diverge outwardly. Alternating with these are five much smaller 

 plates, the basal plates of the supramarginal columns which appar- 

 ently bore no spines. The disk plates within this ring are small and 

 not all seen. They contain apparently a ring of ten plates adjoining 

 the large ring and a central disk plate, and between these very small 

 accessory plates. The interbrachial area of the disk is occupied by 

 small accessory plates and two large marginal plates which extend 

 into blunt, thick, oblique spines. The arrangement of the plates on 

 the abactinal side of the rays is very striking. Radial ossicles 

 (which are elongate, subquadrangular or subellipticaD alternate 

 with a pair of subcircular accessory plates each. The supramar- 

 ginal plates are large, wedge-shaped, adjoining the accessory plates 

 with their narrow ends and leaving deep subtriangular interspaces 

 between them. Outside of the round margins of the supramarginals 

 are the crescent-shaped upper portions of the inframarginals which 

 bear long, slender, articulated spines. Also the first three radials 



