110 NATURAL HISTORY BULLETIN 



Inferomarginal plates large, roundish, with one or two mar- 

 ginal series of sharp, divergent, stout spinules, and a central 

 larger one. Sometimes there are three to five central spinules 

 on the dorsal plates and on the row of plates next to the adoral 

 plates. Pedicellariae small, narrow, elevated, spatulate in form 

 and rather numerous on the dorsal side. 



Station 295, Blake Exped., 115 to 180 fathoms. This species 

 was also taken by the Albatross in the West Indies. 



This species, for lack of duplicate specimens, has not been dis- 

 sected to ascertain the presence of dorsal connective ossicles, and 

 therefore it is referred to Mediaster with some doubt. 



Mediaster (f) agassizU Verrill, op. cit., 1899, p. 181. 



This species was also taken in the West Indies by the Blake 

 Expedition, but the locality and depth are unknown. 



Genus Rosaster Perrier. 



Fentagonaster (pars) Perrier, op. cit., p. 22, 1881; Etoiles de Mer, p. 238, 



1894. 

 Bosaster Perrier, Exped. Trav. et Talisman, p. 386, 1894. Verrill, Eevision 



Genera, p. 197, 1899. Fisher, op. cit., 1911&, p. 164. 



Stellate with slender rays and large disk, marginal plates 

 large, regularly paired, covered with spinules; no spines on 

 dorsals. 



It has rounded, columnar, paxilliform abactinal plates (para- 

 paxillffi), covered, like the marginal and interactinal plates, with 

 small spinules. Most of the superomarginal plates of the rays 

 are in contact medially. 



The inferomarginal plates are spinulose and agree in number, 

 position, and nearly in form with the dorsals. Interactinal 

 plates are thick, closely arranged in two or more chevrons on 

 the triangular interradial area ; each row has an impaired median 

 plate; they are spinulose. 



Adambulacral plates do not have a prominent inner angle. 

 They bear a straight furrow-series of four or five slender spines, 

 and on the actinal surface two or three larger erect spines, which 

 form a regular row. Superambulacral plates are small. Fos- 

 sate pedicellariae with spatulate valves are often present on the 

 dorsal plates; smaller erect ones sometimes occur on the mar- 

 ginal and adambulacral plates. 



