REVISION OF PALEOZOIC STELLEROIDEA. 77 



as in Devonaster. The pieces of the radial columns in Mesopalseaster 

 adjoin one another and are not separated by intercalary plates, nor 

 are these nearly so numerous between the radial and supramarginal 

 columns as in Devonaster. These accessory plates in Devonaster are 

 also irregularly disposed and not in columns as in Mesopalseaster. 



The name Argaster has not been denned nor is it mentioned in such 

 a way that anyone will recognize that Hall intended it for a new genus 

 or subgenus. In addition, its genotype (Asterias antiqua = Mesopalse- 

 aster (?) antiguus) is a poorly known species. Under these circum- 

 stances, and the additional one that the name Argaster never has had 

 any standing as a genus, it should not now be rehabilitated by 

 paleontologists. 



MESOPALSEASTER SHAFFER! (Hall). 



Plate 8, figs. 1, 2. 



Palseaster sha/eri HALL, Twentieth Rep. N. Y. State Cab. Nat. Hist., 1868, p. 284; 

 rev. ed., 1868=1870, p. 326, pi. 9, fig. 1. MEEK, Geol. Surv. Ohio, Pal., vol. 1, 

 1873, p. 66, pi. 4, fig. 1. 



Original description. "Body of about medium size composed of 

 five tapering, acutely pointed rays, which, in the specimen examined, 

 measure seven-eights of an inch from the center of the disk to the 

 extremity. The lower side of the ray is formed of two ranges of plates 

 bordering the ambulacral groove. The marginal range consists of 

 moderately convex plates which gradually decrease in size from the 

 base to the extremity of the ray, 22 or 23 in number [not more than 

 20 exist in any ray of the type-specimen], besides a small terminal 

 one at the angle of the range; each plate of the marginal range is 

 marked on its outer surface by a comparatively large cicatrix for 

 the attachment of a strong spine. The inner range of plates (adam- 

 bulacral) are somewhat smaller, about the same in number, alternat- 

 ing with those of the marginal range; the basal pair (oral plates) 

 are elongate-triangular, and slightly constricted near the middle. 

 Ambulacral a,reas narrow, composed of a double range of poral plates, 

 which at the middle of the ray are about of equal length and breadth. 

 Pores not observed. [The writer could not make out these plates in 

 the type-specimen and believes those described to be the inner sides 

 of the actinal plates.] Upper surface of the ray composed of three 

 ranges of subnodose plates, the outer ranges bearing a strong spine 

 on each plate; the central range apparently destitute of spines. No 

 spines have been observed, but the plates are strongly carinate or 

 pointed." 



Emended description. The largest specimen in the Harris collec- 

 tion measures: B, = 19 mm., r 5.5 mm., R = 3.5r. Another specimen 

 of the same collection: R = 16 mm., r = 5 mm., R = 3.1r. The 

 smallest known specimen in the Vaupel collection: R = 6.5 mm., 



