ASTEBOIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 91 



DrPSACASTER BOREALIS Fisher. 

 PI. 12, figa. 1, 2; pi. 13, fig. 1; pi. 14, fig. 2; pi. 52, figs. 2, 2a, 6. 

 Dipsacaster borealis Fisher, ZooI. Anz., vol. 35, March 29, 1910, p. .546. 



Diagnosis." — Similar to D. eximius in preneral form, but rays more evenly 

 tapered. Rays broad at base; interbrachial arcs abruptly rounded; abactinal sur- 

 face nearly plane. R = 117 mm.; r = 51 mm.; R = 2.3 r. Breadth of ray at base, 

 60 mm. (n;reatcr than r). Abactinal paxillse rcojularly arranged as in eximius, but 

 smaller, and not conspicuously larfjer along median radial area and center of disk; 

 in latter area they may be even a trifle smaller; spinelets not so numerous as in 

 eximius and not extending far down pedicel of paxilla. Pai)ul£)e generally distrii)- 

 uted, si.x around each lobed plate; median radial series of plates not conspicuously 

 lobed as in eximius, but placo<l close together; not surrounded by more than si.x 

 papulae. Marginal plates massive, the infcromarginals defining contour of ray; 

 superomarginals coveretl with low granules compactly placed, and on distal portion 

 of ray, bearing one or two inconspicuous tubercles; infcromarginals covered with 

 imbricating scale-like granules becoming more or less flattened tubercles on outer 

 aboral edge; the covering much more compact and resistant than in eximius; spe- 

 cialized ridges of infcromarginals thicker, and fasciolar furrows narrower than in 

 that species. Adambulacral plates with four to si.x long, stout, round-tipped furrow 

 spines, the four largest flattened with side to furrow; on actinal surface about six to 

 nine spinelets in two series, or without regularity. Actinal intermediate areas 

 smaller than in eximius, especialh' on rays; the plates strongly carinated, bearing a 

 compact group of broad scale-Uke spinelets, surrounded by a row of slenderer curved 

 spinelets. 



Description. — By comparing the largest specimen Mith that of D. eximius, the 

 rays, although very broad, are seen to be less arched in contour; that is, they taper 

 more evenly. The paxilla? are decidedly less compact than in eximius and more 

 uniform in size across the disk or across the ray. They are arranged in regular 

 oblique transverse rows except along the median radial area and center of disk. But 

 unlike those of eximius they are not larger on these areas, being, if different, slightly 

 smaller in center of disk. Thus when the two species are placed side by side the 

 abactinal area has a difi'erent facies. It is true that the paxilla^ along the meilian 

 radial area are the largest on ray, but they grade so evenly into the lateral paxillse 

 that the dilference is not so noticeable as in eximius. The paxillse themselves are 

 individually smaller than in eximius and the spinelets fewer. These are grouped in 

 a compact bunch at the tip of the shorter pedicel, are seventy to eighty in number 

 on largest paxillse, and do not extend very far down the pedicel. The median spine- 

 lets are blunt, but those on sides are pointetl and successively shorter. The spine- 

 lets are relatively shorter. Probably a comparison of the figures (pi. 52, figs, la, 2a) 

 of representative paxillse dra\vn on the same scale will show the striking difference, 

 as well as the fundamental or " generic " similarity. The paxillse covering madreporic 

 hotly are two or three times larger than the othere. Opposite first four superomar- 

 ginals are eleven to thirteen rows of paxillse. 



oFrom type. 



