DISCOVERY REPORTS 



49 rays, R 185 mm. (St. 1955) ; 50 rays, R 180 mm. (St. 167). So far as I am aware this 

 is the greatest number of rays observed in any sea star and is sHghtly in excess of twice the 

 maximum number (24) ever reported for the large north Pacific Pycnopodia helianthoides. 



The outstanding characters of this species are the very large crossed pedicellariae 

 carried by the abactinal transverse integumentary welts of ray ; and the rapid atrophy of 

 the abactinal skeleton beyond the proximal third of the ray. At first the longitudinally 

 oriented ossicles of the skeleton disappear leaving rather widely spaced transverse 

 arches of slender plates, corresponding to the lateral pairs of marginals. Then the 

 abactinal elements of these arches disappear, leaving the marginal plates, which become 

 smaller and smaller as end of ray is approached. On the outer third of ray they are 

 scarcely more than rudiments. A very small inferomarginal spinelet persists nearly to 

 end of ray but is quite hidden by the thick integument and pedicellariae. 



The transverse welts, or thickening, of the integument, which proximally overlie the 

 skeletal arches, are continued to the end of the ray and are more prominent after the 

 disappearance of the abactinal plates. These heavier cushions distal to the region of more 

 or less complete abactinal skeleton carry the largest pedicellariae in considerable numbers, 

 as shown by Koehler's figures (1917, pi. i, figs. 2, 4). Over the proximal, so-called 

 genital area, the crossed pedicellariae are fewer and smaller, their place to some extent 

 being taken by numerous large and small laceolate straight pedicellariae. 



On fully grown specimens (e.g. with R 180 mm.) the characteristic large crossed 

 pedicellariae are 1-1-5 mm. long and on the largest examples upward of 175 mm. long 

 (Fig. I, 3). On the marginal spines and proximal abactinal plates are numerous smaller 

 pedicellariae approximately 0-4 mm. (Fig. 3 c); and on the outer adambulacral spines a 

 cushion of still smaller ones, o-25-o-3 mm. (Fig. 3Z)). 



Crossed pedicellariae are practically absent from the disk, but in place of them are 

 very numerous small and large lanceolate straight pedicellariae, the largest as long as the 

 acicular spinelets but much thicker. 



Sladen does not mention the mouth-plates. They are more easily observed in small 

 than in large specimens, for in the latter the entire circumference of actinostome is a 

 cheval-de-frise of crowded spines and very numerous large straight pedicellariae which 

 hide the plates. In a small specimen, with disk-diameter 25 mm. and 36 rays, the inner 

 end of all but 5 of the ambulacral furrows is bridged by a fusion of the inner lateral 

 angles of the mouth-plates of either side of furrow. In a large specimen with 49 rays 

 only 4 furrows are open at the inner end. This is obviously caused by a crowding of the 

 mouth angles. The organic bridge consists at first of tissue only, but as growth proceeds 

 the opposing plates are wedged tightly together so that at best only a narrow suture 

 separates them. In old examples actual ankylosis takes place. In early stages a sort of 

 epineural tube represents the inner end of the ambulacral furrow, but in later stages of 

 fusion this tube is often very small— so small in fact that one wonders how the radial 

 nerve avoids compression during active movements of the animal. The armature of the 

 plates is variable, partly due to suppression of the lateral marginal spines by this fusion. 

 Each plate has on the actinostomial margin adjacent to median suture a prominent 



