ASTEROIDEA OF NORTH PACIFIC AND .U)JACENT WATERS — FISUER. 341 



KEY TO THE KNOWN GENERA OP KORETURA8TERIUj£. 



Abactinal plates polygonal or roundLsh in outline, the epinc» composing the paxillifonn tiifi.i naked 

 and free KoTethrasUT Thi)mi>i»on. 



Abactinal plates cruciform forming wide meshes; the spines composing the paxilliform tufts in 

 membranous sacs which are united together in the interior of the group PeribolaaUr Sladen. 



Genus PERIBOLASTER Sladen. 



PeribolasUr Sladen, Narr. Challenger Exp., vol. 1, 1885, p. 616 (no type-species); Challenger 

 Asteroidea, 1889, p. 46-1. Type, P./olliculatus. 



Diagnosis. — Koretbrastcridse liaviiig the abactinal surface paved with cruci- 

 form plates whose ilelicate lobes are connected bj' supplementary ossicles forniin;^ 

 a fairly regular network of largo quadrangular meshes over the entire surface. 

 On the center of each primary abactinal plate is borne on a small boss a fascicule 

 of delicate, subeciual spinelets, enveloped in membranous sheaths, united in the 

 interior of the fascicule. One to several papuhe present in each mesh; no actinal 

 papuljB. No actiinil intermediate plates. Adambulacral armature forming with 

 that of the inferomarginal plates a transverse series of four to si.\ large single 

 isolated spinelets invested with membranous sacs. Mouth i)lates fairly large, of 

 the type of the Pterasterida-, and with a prominent median keel, a few marginal 

 and a single or no suboral spine. Tube feet in two or four rows, with Hesh^' button- 

 like terminal disk. No pedicellaria. 



PERIBOLASTER BISERIALIS Flataer. 



PI. 97, figs. 1, 2; pi. 114, figs. 3, Sa-c; pi. 115, fig. 5. 



PeribolasUr biserialis Fisher, Bull. Bur. Fisheries for 1904, vol. 24, June 10, 1905, p. 313. 



Diagnosis. — Differing from P. foUiculatus Sladen in having the tube-feet in 

 two series, in having a much larger disk and relatively shorter rays, a more open 

 abactinal skeleton, with fewer and more widely spaced primary jjlates, and longer 

 spinules; adambulacral plates with three and inferomarginals with a single spine, 

 the four forming a single transverse series (sLx in foUiculatus) no suboral spine 

 as in folliculatus. K = 25 mm.; r=10 mm.; R = 2.5 r. (Type, R = 20 mm.; r = 

 7.5 mm.; R = 2.6 r; breadth of ray at base, 8.5 mm.) Abactinal surface convex, 

 rather flexible; form stellate; rays rather short and robust, wider than liigh, 

 tapering, the outer part somewhat slender and often recurveil; interbrachial arcs 

 acute, the raj's being constricted slightly at the base; edges of ray rounded, due 

 to inflation of abactinal integument; tube feet strictly biserial. 



Dtscripiivn. — Abactinal jilates ordinarily obscured by the skin unless dried. 

 These plates are usually four- (sometimes three-) lobed, the lobes being con- 

 nected by rod-like intermediate ossicles tj-pically longer than the lobes them- 

 selves, forming a very open reticidate skeleton with wide iuters])aces for the pa|)ula<. 

 No serial arrangement of plates is very apparent but they are nevertheles-s in fairly 

 regular order, there being in the largest example about live longittuiinal .series 

 of plates. The plates of adjacent rows alternate and tlie papular areas are (piad- 

 rate. Each plate has a slight eminence or tabidum surmotmfed by a brush-liko 

 fascicule of three to live delicate, gla.s,sy, sharp spinules about 3 mm. long, which 

 are united into a compact group by a membrane, the bpLuules sometimes radiating 



