ASTEEOIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 41 



t'. Actinal interradial areas fairly extensive with numerous intermediate plates arranged in 



definite series extending from adambulaerals to inferomarginals; (actinal intermediate 



plates occupying 50 per cent or more of minor radius, measured on dorsum, bvit marginals 



not greatly unlike in size, nor inferomarginals extending laterally beyond the 



siiperomarginals). 



/'. Madreporic body hidden by special paxillse on its surface; inferomarginal plates and 



sometimes superomarginals with a single stout erect spine or spinule; abactinal paxilla; 



only slightly lobed, or polygonal, not markedly stellate, .\dambulacral armature not 



a^stropoctinoid; furrow spinelets in a regular comb Plulonaster Sladen. 



• p. Madreporic body naked and large; adambulacral armature astropectinoid ; abactinal 



plates stellate; marginal spinulation variable but not as above. 



gK Inferomarginals with large flattened spatulate spinelets, chisel-shaped, roundish or 



square cut at tip, closely packed, with here and there a transverse row of five, but 



usually without order; actinal intermediate plates closely packed with stout flattened 



spatulate spinelets. Paxillse with long pedicels and compact crowns of short 



inbending spinelets Moirastera Sladen. 



g^. Inferomarginals with a single transverse row of pointed spines in addition to much 



smaller papilliform or squamiform spinelets; actinal intermediate plates with clusters 



of papilliform or granuliform spinelets, separated by deep fascioles; paxills with 



only moderately long pedicels, sometimes short, the spinelets forming a distinct 



central group surrounded by a peripheral series; adambulacral plates separated by 



fasciolar grooves. 



A'. Gonads extending far along ray, on either side; a distinct medioradial series of paxillae, 



slightly larger than two or three adjacent series (especially on outer part of ray); 



adambulacral fascioles shallow; deposits in tube feet; first adambulacral plate 



considerably compressed; central actinal adambulacral spinelets not increasing in 



length toward end of ray; madreporic body moderately large Tethyastcr S<\i.Aen. 



h-. [Gonads imknown]; no definite medioradial series of paxillse slightly larger than 

 those adjacent (?); adambulacral fascioles deep, densely lined with small delicate 

 spinelets; stoutest actinal adambulacral spine increa.sing in size toward end of 



ray; madreporic body very large Siderinslerb Verrill. 



<P. Superomarginal plates thin and confined to side wall of ray; no fascioles between them. 

 c'. Marginals with a single, rigid, sharp, perpendicular spine; madreporic body large with 



paxillse on its surface Dylastcrc Sladen, p. 101. 



e^. Marginal plates excessively thin and confined to side wall of ray, both series with a vertical 

 series of five or more appressed flattened spines; madreporic body small, naked. 



Ripaster Koehler. 

 b'. The two series of mai^inal plates unequal in size, often forming an angulated rather than vortical 

 margin to ray; superomarginals much smaller than inferomarginals or at least confined wholly 

 to abactinal surface on rays; inferomarginals often extending laterally beyond superomarginals, 

 thus defining the border of rays (an exception in Loncholaslcr) . 

 c'. Madreporic body not large and hidden by special paxillse on its s\irface; anal aperature very 

 small, or absent, 

 d'. No well-developod s-eries of plates between inferomarginal and adambulacral series throughout 

 ray (rudimentary at base of ray in Ti-itonaster). 

 c'. Superomarginal plates not conspicuously smaller beyond middle of ray. Marginal fascioles 



well developed Astropectcn Gray, p. 55. 



C-. Superomarginals very much reduced in size on outer part of ray; inferomarginals very tumid 

 with an oblique series of long seta-like spines; no marginal fascioles. . . Tritonasler Fisher. 



a Sladen, Challengrr Asteroidea, 1889, p. 192. Type, ArchasUr magnificits Bell, Ann. and Mag. Xat. 

 Hist., ser. 5, vol. 8, 18S1. p. 4-10; see Koehler, Trans. Roy. Soc. Edinburgh, vol.46, 1908, pt. 3, p. 630, pi. 

 12, figs. 107-110. 



6 Verrill, Trans. Conn. Acad., vol. 10, 1899, p. 219. Type S. (/ran(fi's Verrill. The genus is very 

 closely related to Tethyasler. 



c Includes Crcnastcr Perricr, not d'Orbigny, 



