346 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



PTERASTER MILITARIS (O. F. MUDer). 



PI. 98, figs. 1, 2. 



Aslerias militaris O. F. Muller, Zoologia Danicse Prodromus, 1776, p. 234. 



AsterUciis militaris Muller and Troschel, System der Asteriden, 1842, p. 44. 



Pleraster militaris Muller and Troschel, System der Asteriden, 1842, p. 128, pi. 6, fig. la and 



6.— Fisher, Ann. and Mag. Nat. Ilist., ser. 8, vol. 5, Feb., 1910, p. 167. 

 Pleraster aporus Ludwir, Echinodermen des Beringsmeeres, Zool. Jahrb., Abth. f. Syst., vol.1, 



1886, p. 293; Fauna Arctica, vol. 1, 1900, p. 470, footnote.— Clark, Bull. Mus. Comp. Zool., 



vol. 51, No. 11, 1908, p. 287 (key). 



For an extensive list of references (none referring to the region covered by this report), see 

 Ludwig, Arktische Seesterne. Fauna Arctica, vol. 1, p. 469. 



Diagnosis. — Rays five. R = 2 to 2.5 r. Form stellate, rays evenly tapered, 

 often slender at tip; supradorsal membrane fairly thick, without muscle bands, 

 crowded with calcareous deposits in the form of minute very spiny fenestrated or 

 reticulate bodies; spiracula few, fairly large, scattered whole length of ray abac- 

 tinally and on sides; pedicels of pseudopaxillse low, slightly higher than broad, with 

 three to five slender spines. Adambulacral plates, proximally, \\-ith a transverse 

 webbed comb of seven to nine spines (according to size of specimen), the free edge 

 of web being slightly thickened, undulating, and continued outward as a ridge on 

 the actinolateral membrane. Mouth plates with six to eight webbed marginal, and 

 a single stout suboral spine, sheathed in membrane, and with a clear glassy tip. 

 Actinolateral membrane narrow with a free margin. 



Notes on North Pacific specimens. — An example, station 2846, has the following 

 measurements: R = 75 mm.; r = 33 mm.; R = 2.2 + r; breadth of ray at base, 38 

 mm. A specimen from station 3445 is about the same (large) size. 



The calcareous deposits in the supradorsal membrane can be readily seen with 

 a strong glass, without clearing. The membrane itself is fairly thick, especially in 

 the large example from station 2846, and is wTinkled more or less. The spines form 

 only slight protuberances. The adambulacral combs are very regular, and the man- 

 ner in wliich their web is continued laterally across the actinolateral membrane is 

 characteristic of all the Pacific specimens. In very small examples this continua- 

 tion is for only a short distance toward the margin, but in the large ones it forms a 

 ridge nearly to the border. In three specimens accidentally dried these ridges are 

 largely obhterated. The inner adambulacral spine is very short, the next one or 

 two successively longer, so that tlie third or fourth is nearly as long as the longest, 

 which are the following four or five. The large specimens have eight or nine adambu- 

 lacral spines, while the small ones have about seven on the proximal half of ra3^ 

 None of the spines have a terminal membranous sacculus as in Pt. jordani, but the 

 edge of the web is, in life, slightly thickened and emarginated between the spines 

 as in Pt. stellifer Sladen. The only Atlantic specimen of militaris available (from 

 Bay of Fundy) has stouter adambulacral spines, six or seven in number, but the 

 specimen is small (R = 30 mm.). The mouth plates have six to eight slender gradu- 

 ated webbed marginal spines, but the companion combs are not joined. The long 

 inner spine is longer than the median suture of jaw plates. The suboral spine 

 is clavate, pointed, very much heavier than any other spine, has a glassy distal 

 part, and is normally sheathed in membrane. In the largest specimen this spine 



