ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 357 



The suboral spine is sharp and glassy, the outer half fltirint;, witli three sharp 

 edges and three coneave faces which can be easily discerne<l even when the spine 

 is sheathed in membrane. The shape of this spine, which is situated on a boa'^, 

 at about the middle of the plate, is similar to that of trigonodon. 



Actinolatoral membrane wide, with a wide fringe defining the entire ambitus. 

 About the seventli actinolateral sjiine is longest in type; thence they regularlv and 

 rapidly decrease in length toward the tip of ray. When viewed from above, the 

 membrane projects a conspicuous distance (about one-sLxth width of ray) beyond 

 the edge of the supradorsal membrane. Edge of membrane scalloped; spines 

 showing through membrane. 



Color dirty whitish, or brownish gray in alcohol. 



Type.—Q&i. No. 27793, U.S.X.M. 



Type-locality. — Albatross station 4784, near Attu Island, Aleutians, l.'i.'j fathoms, 

 coarse pebbles. 



Distribution. — Known only from the vicinity of the Aleutian Islands. 



Specimens examined. — From type-localit}-, two; from station 3223, near 

 Unalaska, 56 fathoms, black pebbles, three specimens. 



Remarls. — Superficially, at least, this species resembles puhnUus, especially 

 the abactinal view, the groups of spines forming slightly raised independent spiny 

 protuberances. The differences are as follows: Low pa.xillar pedicels with spines 

 much longer (reverse in pnlvillus), no muscle bands between spines (figured in 

 pulmllus), adambulacral spines fewer (five); aperture slits of a peculiar and charac- 

 teristic form; mouth spines five; suboral spine not slender but stout and three- 

 edged. The deposits in the supradorsal membrane may constitute a further difler- 

 ence ( I have not seen Atlantic specimens of pulviJlus) . From Pttraster ohesns Clark 

 (Sagami Bay, Japan) temnochiton differs in having calcareous spicules in mem- 

 brane, low paxilliv with fewer spines, fewer adambulacral spines (six or seven in 

 obesu-s). In contrast to temnochiton, obesus has independent oral spines (five to 

 seven), short actinolatoral spines, so that the fringe is narrow and concealed from 

 above. Even the suboral spine is different, that of obesus ending in a triangular 

 point, while in temnochiton the spine is really three-e<lged for a considerable part 

 of the length. The aperture papilla is small in obesus, an<l the aperture is not 

 unusually large, as in temnochiton. From triynnodon, temnochiton differs in having 

 a wi<le, not narrow, actinolateral membrane, differently formed deposits, low, 

 not high paxillip, slender ant! long, not short and thick aperture papilla>, in having 

 the outer adambulacral spine distant from, not close t<> the actinolateral membrane, 

 in having nuich more conspicuous apertures, in having companion combs of oral 

 spines bound together mesially by a continuous web. The abactinal facies of the 

 two is quite different; the lateral fringe, for one thing, does not define the ambitus 

 in Irigonodon. 



