ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 381 



Piixilhv with usually four spines (soniotimos throo, rarely five), whicli i)u.sh uj) 

 the membrane (no central spine), the individual iin.xilla- being easily di.stinpuishable 

 and arranged in nine rows along each ray, the |)a.\illa' of adjacent rows alternating 

 in a regular manner. Spiracula varying greatly in number according to age. 

 In the immature type from off San Diego they are not numerous and are ven.- 

 inconspicuous, but in the adult Alaskan examples they are very luimerous though 

 small. In the smallest of these examples (R = 10 mm.) s|)iracula are \ory much 

 fewer than in the largest. (See paragraph on young, below.) The spiracula when 

 fully develoiied are exceedingly numerous all over the supradorsal membrane both 

 between the pa.xillar crests and amid the spines, from the tops of which they tend 

 to arrange themselves in radiating lines. They are thus not in definite areas, 

 e.xcept on the interbrachial web, where the sjjiracula form parallel linear areas 

 extending outward from the paxillar region. These hnes occur from the inter- 

 brachial angle (the longest Une being fourth or fifth from angle) nearly to tip of 

 ray. As tliis fringing membrane is usually contracted these areas are then invisible 

 and were entirely overlooked in the type wliere they can not be seen. The spiracula 

 are not present between the spines of a paxilla crest in all the Alaskan specimens, 

 being absent in those from station 2859. Oscular orifice large; valves triangular with 

 a truncate summit, liowever; spinelets about eleven to sixteen to each valve, the 

 seven or eight central ones subequal, the laterals graduated: membrane of valves 

 rather thick; on base of each valve at either side a well-defined triangular spiracular 

 area about one-third the height of the longer spines, containing many spiracula; 

 in the membrane between adjacent valves numerous spiracula, which extend 

 nearly to the distal edge of the valves; supradorsal membrane slightly raised along 

 interradial lines in examples with refle.xed rays. 



Adambulacral spinelets Ihittened, tapering, sharp, in an oblique transverse, 

 slightly curved comb of four or five, the outermost longest and most adorally placed, 

 the rest graduated in length toward the inner, which is one-third to two-thirds 

 smaller. Just external to the outermost and in line witli the series is the broadly 

 ovate, round-tipped aperture papilla, fitting tightly over the corres|)onding seg- 

 mental aperture hke a valve, the base of this papilla abruptly narrowed for articu- 

 lation to the plate; the first papilla much larger than the rest and hnng in the actino- 

 lateral membrane. In Bering vScii specimens the tip of some of the papilla?, 

 especially ])roximally, is pmlonged in a narrow membraneous sacculus or flap 

 one-third to one and one-half the length of papilla. The outermost spine of the comb 

 also has a fleshy tip of variable length. These sacculi are not present in the type, 

 but that is a young specimen and the sacculi are very deciduous. Moreover, the 

 Alaskan examples are not constant in this character as pointed out under " Young." 

 on page 382. 



The combined mouth jilates are higher and narrower than in typical species 

 of this genus. The medium suture is on the summit of a «entral eminence or keel 

 of the combined plates, which slope off steeply on either side to the margin next 

 to furrow. The actinostomial margin is slightly curved and slopes downward from 

 the median suture and forms a rounded angle at the mouth of furrow. At tliis 

 point is the greatest width of the combined jdates. On this sloping free margin of 



