REPORT ON THE ASTEROIDEA. 23 



Genus Pontaster, Sladen. 

 Pontaster, Sladen in Narr. Chall. Exp., 1885, vol. i. p. G10. 



Disk small. Rays long and tapering. 



Marginal plates forming a definite vertical wall or a well-rounded margin. Often 

 elongately oval, or subtriangular in form. The two series have a tendency to alternate 

 more or less, which causes the horizontal margin that touches the companion series of 

 plates to be more or less definitely angulated or to form two facets. Supero-marginal 

 plates usually with one prominent well-developed spine. Infero-marginal plates with one 

 to three similar prominent spines. On the general surface of the plates of both series are 

 borne minute spiniform granules or miliary spinelets. 



Abactinal area with round squamiform plates, bearing more or less well-defined 

 paxillse. No definite order of arrangement. Papulae confined to an area at the base of 

 the ray, frequently associated with a special calcareous structure of the skeleton — the 

 papularium. 



Actinal interradial areas with very few intermediate (ventral) plates. 



Armature of adambulacral plates consisting of: — (1.) a semicircular furrow series of 

 small spines; and (2.) one to three outer spines on the actinal surface, usually larger and 

 conical ; and a few miliaries may also be present. 



Madreporiform body small, usually near the margin, but sometimes nearly midway 

 between the margin and the centre of the disk. 



Pedicellarise frequently present, sometimes comb-formed, sometimes quadrivalvate, 

 sometimes bivalvate. 



Remarks. — -The type of this genus is the starfish originally described by Diiben and 

 Koren 1 under the name of Astropecten tenuispinus, which was subsequently referred by 

 Sars 2 to the genus Archaster, a determination which has been followed by the majority 

 of the succeeding writers. Reference has already been made (p. 1 of this Report) to 

 the incongruous character of the assemblage of species that have been included in the 

 genus Archaster of Miiller and Troschel, and in my remarks under the head of that genus 

 (below, p. 121) will be found a further expression of my views as to the only species that can 

 be retained under the generic name of Archaster. These conclusions are arrived at after 

 a careful study of the structure and anatomy of the forms ; and in the present place it is 

 unnecessary to recapitulate the grounds upon which the limitation of the genus is based. 

 A glance at the diagnosis of the genus given above, and of that of Archaster (sensu stricto) 

 as formulated on a subsequent page, is sufficient to indicate that the two types are widely 

 separate and can certainly not be classed as factors of the same generic term. 



1 K. Svensk. Vetensk.-Akad. Handl, Ar 1844 (1846), p. 251, pi. viii. figs. 20-22. 

 - Ovcrsigt af Norges Echinodermer, Chiistiania, 1861, p. 38, pi. iii. figs. 5-7. 



