bo 
bo 
THE VOYAGE OF H.M.S. CHALLENGER. 
Actinal interradial areas small, with numerous small intermediate plates which extend 
far along the ray. The intermediate plates all bear small compact groups of spinelets. 
Armature of the adambulacral plates consisting of :—(1.) a furrow series of rather long, 
delicate, cylindrical, uniform spinelets, which form either a straight series or may be 
slightly curved. (2.) On the actinal surface of the plate are two longitudinal series of 
shorter and more compressed spines, the inner of these two series being frequently irregular. 
Madreporiform body large and situated rather nearer the margin than midway between 
it and the centre of the disk. 
No true pedicellarie are present, but an incipient form of the organ may occur in some 
species. 
Remarks.—The type of this genus is the starfish originally described by Miiller and 
Troschel! under the name of Astropecten andromeda. It appears to me to merit generic 
distinction on account of the difference (1.) in the character of the marginal plates, (2.) 
in the number and disposition of the actinal intermediate plates, (3.) in the armature of 
the adambulacral plates, (4.) in the spinulation of the marginal plates, and (5.) in the 
character of the paxille. 
Synopsis of the Species included in the Genus Psilaster herein described. 
A. With marginal plates vertical, almost confined to the lateral wall of the ray. 
a. With narrow delicate rays. Interbrachial arcs well rounded. With papilliform 
eranules on the marginal plates: no membrane. Inner pair of mouth- 
spines very large. c 5 : : . : : 3 gracilis. 
b. With robust rays, thick at a tea Interbrachial arcs acutely rounded. With 
squamiform papille on the marginal plates, often covered with membrane. 
Inner pair of mouth-spines small. 
a. Infero-marginal plates at the base of the ray with four or five flattened 
spinelets equally spaced on the aboral margin. Inner pair of mouth- 
spines subequal to the rest. Supero-marginal plates conspicuously 
encroaching on the abactinal area on the outer part of the ray : andromeda. 
b, Infero-marginal plates at the base of the ray with three or four small flat- 
tened spinelets grouped in a slightly oblique series near the aboral 
end of the lateral margin. Inner pair of mouth-spines conspicuously 
longer than the rest. Supero-marginal plates not conspicuously 
encroaching on the abactinal area on the outer part of the ray . acuminatus. 
B. With broad marginal plates, forming a broad, conspicuous margin to the abactinal area. 
a. With marginal plates; nearly plane. Supero-marginal plates with no specially 
enlarged tubercle.; Infero-marginal plates with one spine near the lateral 
margin. No pedicellarize on the marginal plates 2 3 . cassiope. 
b. With marginal plates distinctly tumid. Supero-marginal lates often with a spe- 
cially enlarged tubercle. Infero-marginal plates with an oblique series of four 
spines near the lateral margin. Incipient pedicellarie on the marginal plates, patagiatus. 
1 System der Asteriden, 1842, p. 129.° 
