350 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



PTERASTER JORDANI Fisher. 



PI. 100, fit; 2\ pi. 101, fij;. 1; pi. 117, fifre. 1, \a-h. 



Pterasler jordani Fisher, Bull. Bur. Fisheries for 1904, vol. 24, June 10, 1905, p. 314; Ann. and 

 Mag. Nat. Hist., Bor. 8. vol. 5, Feb., 1910, p. 67.— Clark, Bull. Mus. Comp. Zool., vol. 51, 

 No. 11, April, 1908, p. 286; 



Diagnosis. — Similar in general form to Pteraster militaris, but snpradorsal 

 membrane lacking spiny calcareous bodies, tube feet in four instead of two rows, 

 only three or four adambulacral spines, four mouth spines, and two (one to three) 

 paxiilar spines. R = 2 r. 



Description. — Rays five. R = 75 mm.; r = 37 mm.; R = 2 r. Breadth of ray 

 at base, 37 to 42 mm. Thickness of ray at base, about 28 mm. (type). 



Form stellate, depressed; abactinal surface of rays and disk convex, actinal 

 surface subplane; edges of ray rounded; rays tapering, with fairly straight sides, 

 bluntly pointed, though sometimes swollen near tip and the extreme tip recurved, 

 giving an entirely different appearance; interbrachial angles obtuse; a well devel- 

 oped lateral fringe present, though actinolateral membrane is narrow. 



Supradorsal membrane rather thin, with no deposits of calcareous matter; 

 paxiilar spines very prominent; two spines to each pseudopaxilla (sometimes one 

 or three), one considerably longer than the other, protruding 3 or 4 mm. above 

 general level of the membrane, but carrying the latter with it; pedicel very low, 

 and the spine correspondingly rather longer than usual in this genus; fine criss- • 

 crossing muscle fibers exceedingly abundant, and the summits of the paxiilar 

 spines connected by faint muscular bands, which are nearly invisible in the type- 

 specimen but show with some distinctness in a smaller example; in the irregular 

 meshes thus formed one to three large spiracula, these often absent; oscular orifice 

 rather small, though variable in size; valves with a much higher and stouter pedicel 

 than other pseudopaxillse, and with about fourteen spines in two series on top of 

 pedicel, all united by single membrane. The pedicel is about 2 mm. high in the 

 midradial region of the type, the entire pseudopaxilla being about 11 to 12 mm. 

 high. The papulae extend about 5 mm. up the pseudopaxilla and have numerous 

 short lobes at the top. 



Adambulacral plates wuth a transverse series of tliree spines and one spinelet, 

 united by a web; inner member of the series quite small and situated slightly 

 aborad from the others; the next three are two to five times longer, and increase 

 slightly in size outward, being united by membrane nearly to their tips, which are 

 capped by a membranous sacculus; outer spine close to the corresponding actino- 

 lateral spine, to which it is united by membrane. Aperture papillae prominent, 

 jawbone-shaped, free on the aboral margin. On a smaller specimen the inner small 

 spinelet is absent, and in the type it is sometimes absent, especially on plates beyond 

 the middle of the ray. A specimen from off the coast of Washington also has tlu-ee 

 spines on most of the plates. Thus the combs may contain tliree long and one 

 shorter spinelet or three long subequal spinelets only. The aperture papilla is 

 not tented over by an auxiliary membrane, forming a special pocket between each 

 pair of adambulacral combs. (See next species.) 



