WEST INDIAN STARFISHES 



197 



an odd interradial marginal plate in each series {Prionaster) . 

 Surface of the marginal plates usually smooth or with a few 

 scattered granules, sometimes entirely granulated, usually cov- 

 ered with a thin membrane. 



Interactinal plates form radial series, usually double, running 

 from the adambulacral to the marginal plates, with deep fasci- 

 olated grooves between them, continuous with the fasciolated 

 grooves between the marginal plates. 



The adambulacral plates project over the ambulacral furrows, 

 forming constrictions; they bear a curved or angular series of 

 furrow spinules united by a basal web. 



The jaws are rather large and very prominent, with an open 

 suture. They bear two or more enlarged apical spines, and more 

 or less numerous smaller spinules on the actinal side. 



Genus Prionaster Yerrill, 1899, p. 215. 



This genus differs from Goniopecten especially in having an 

 odd interradial marginal plate, in each row, and a double series 

 of unpaired interactinal plates corresponding to them. 



For more details see the original description. The genus in- 

 cludes only the following species : 



Prionaster elegans Yerrill. 



Prionaster elegans Yerrill, Kevision Genera, op. cit., p. 216, plate; figures 4, 

 4a, 4&, 4c, 1S99. 



Plate xii ; figures 4-4c. 



Disk smaU ; sides high and vertical, evenly incurv^ed ; rays high 

 and nearly square at base, tapering regularly to the slender tips. 



Radii of the type, 14™™ and TO™™; ratio, 1 :5. 



The marginal plates are oblong and much higher than long on 

 the disk, but gradually become squarish on the rays. The upper 

 and lower are exactly coincident, so that the vertical sutures are 

 continuous. Their sides are nearly perpendicular and they en- 

 croach only a short distance on the disk, but at the middle of the 

 rays each series is about as wide as the dorsal area ; distally, near 

 the tip of the rays, they are separated only by a single row of 

 very small paxillae. The distal plates bear groups of small 

 spaced granules near the upper end. Each of the upper ones, 



