ASTEIIOIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 79 



THRISSACANTHIAS PENICILLATUS (Fisher). 



PI. 17, fig. 4; pi. IS, figs. 1-.5; pi. 53, figs. 1, la-e. 



Persephonastcr penicillatus Fisher, Bull. Bur. Fisheries for 1904, vol. 24, June 10, 190.5, p. 297. 



Diagnosis. — Rays five. 11 = 176 mm.; r = 35 mm.; R = 5r. Breadth of ray 

 at base (between second and third superomarn:inals) .36 mm. General form flat- 

 tened; rays long, tapering from a narrow ba.se and in small to medium-sized speci- 

 mens swollen a trifle a])ove base; disk rather small, capable of slight inflation; 

 interbrachial angles roundeil; abactinal integument thin, a trifle convex at base of 

 ray. Paxilliu small, arranged in transverse spaced njws except on center of disk 

 and along midradial line, eacli with a cylindrical ])edicel crowned with a brush-like 

 group of eight to twelve slender needle-like spinclets which are longer than pedicel ; 

 papuhe everywhere except at tip of ray, conspicuous. Superomarginal i)lates 

 thirty-nine, strongly tumid, with a long, stout, tapering spine (.sometimes two) in 

 center, and one or two smaller spines on upper edge; large spines sometimes biild; 

 general surface of plate bristling with small spinelets; iisuaUy one or two j)edicel- 

 lariie present, formed of two to four small sharp spinelets in a circle, these very 

 inconspicuous and sometimes absent; occasionaUy present on inferomarginals. 

 Latter are opposite superomarginals; a few of proximal plates with a transverse 

 series of three stout tapering pointed spines, sometimes, but not always, a trifle 

 flattened and bifid; rest of plates including first two with two such spines; general 

 surface bristling with delicate spaced spinelets, increasing in size toward lower 

 end of plate and summit of transverse ridge; no true marginal fasciolar grooves; in- 

 stead plates slope up gradually from sutures without forming abrupt specialized 

 ridges, as in Astropeden, PsUaster, and others. Adambulacral jilates with five or 

 six (in smaller specimens three or four) furrow spinelets rather delicate and com- 

 pressed, and forming a divergent palmate series, and on actinal surface an enlarged 

 usually flattened blunt spine with a variable number of smaUer blunt membrane- 

 invested spinelets surrounding it or in two longitudinal rows. Mouth plates \vith 

 peculiar furrow series formed of an angular group of about five spinelets situated 

 at a higher level than enlarged tooth; that is, nearer peristome. Actinal inter- 

 radial areas small but plates extending far along ray, and armed with rather deli- 

 cate spaced spinelets, these sometimes forming a pedicellarian apparatus. Madre- 

 poric body large, free; gonads in several tufts (ten to twelve) extending a short 

 distance along ray; superambulacral j)lates very weU developed. 



Description. — The rays are decidedly long in this species and longer in large 

 than in small specimens. Abactinal integument thin, frequently collap.sed on 

 outer part of ray onto the ambulacral ridge. Paxillie small to medium sized, dis- 

 tinctly and uniformh' spaced; arranged in transverse well-spaced series on rays, 

 but without regular order in center of disk and along midradial line. The paxilla) 

 decrease regularly in size distad and toward center of disk, and not so conspicu- 

 ously toward marginal plates, being largest on the radial areas at base of ray. 

 The transver.se rows of paxiUse are quite regular, and l)etwcen them is a double 

 row of conspicuous papula?. Each paxilla consists of an elongate, elliptical base 

 set longitudinally with reference to long axis of ray, surmounted by a stout, cylin- 



