<J2 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



usually in ropular transvcrso lines at sides of ray, and with potygonal or roundish 

 bases- actinal interradial areas small, with numerous small intermediate plates 

 which' extend far along ray, and which bear compact groups of spinelets often 

 subsacculate; papula^ absent from midradial area and center of disk; armature of 

 adambulacral plates, a furrow series of rather long delicate cylindrical or flattened 

 spinelets in a straight or slightly curved series and on actinal surface, about two 

 longitudinal series of shorter mqrc compressed spinelets, sometimes irregular in 

 disposition: anus present or absent; well-developed superambulacrals; tube feet 

 conical without sucking disks; no pedicellaria^. 



Remarks. — This genus differs from the closely related Bathyhiasier in having a 

 rather numerous furrow series of slender subequal spinelets in a slightly curved 

 comb, the outer edge of which is frequently straight; the central spinelet of series 

 is not greatly enlarged, nor is the series very angular as in Bathyhiaster. There is 

 not a flap of integument at the tip of any spinelet, as typicaUy the case with the 

 central spinelet in Bathyhiaster. Sometimes the actinal spines are nearly as saccu- 

 late as in Bathyhiaster. but the marginal spines are much more prominent in Psi- 

 laster. In Bathyhiaster the base of a paxilla is steUate; in Psilaster roundish or 

 polygonal. 



PSILASTER PECTINATUS (Fisher). 

 PI. 7, figB. 5, 7; pi. 10, fi-;9. 1-3; pi. 50, figs. 3, 3a-c. 



Bathyhiaster pectinatus FisnZR, Bull. Bur. Fisheries for 1904, vol. l!4, June 10, 1905, p. 295. 

 Plutonaster abyssicola Ludwig, Mem. Mu.s, Comp. Zool., vol. 32, July 17, 1905, p. 30, pi. 3, figs. 

 13, 14; pi. 19, figs. 102-lOG. 



Diagnosis." — Rays five. R = 73mm.; r=15.5 mm.; R = 4.7 r. Breadth of 

 ray at base, between first and second superomarginals, 16 mm.; midway along 

 ray, 13.5 mm. Rays moderately elongate, tapering continuously from base to a 

 sharply pointed extremity; interbrachial angles rounded; lateral wall, formed by 

 marginal plates, nearly vertical, or sloping inward toward the actinal surface, only 

 the upper end of the superomarginal plates forming a narrow border to paxillar 

 area; abactinal surface slightly inflated on disk usually plane on rays; actinal 

 surface convex; a low epiproctal cone usuaUy present; a very small anal aperture. 

 Paxillai of abactinal area small, not crowded, with about four central stubby spine- 

 lets surrounded by a perif)heral series of ten to fifteen slender ones. Superomar- 

 ginal plates each with a sharp spinule near upper end, on edge of ray, forming a 

 series for two-thirds or three-fourths length of arm ; sometimes two such spinules 

 present; inferomarginals with two spinules, one above the other, the upper forming 

 a series to tip of ray, the lower a parallel series for only about two-thirds length of 

 ray. Adambulacral plates with a furrow series of eight spinelets (seven in smaU 

 specimens) and on actinal surface two or three longitudinal series of tliree or four 

 each, invested in a pulpy saccular sheath. Actinal intermediate areas smaU, the 

 plates beset with compact groups of very fleshy, spatulate, round-tipped papiUfe. 



o From type; important variationB exhibited by other Bpecimens are mentioned, however. 



