224 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.46. 



Family ^lYXASTERID^. 



ASTHENACTIS MEDUSA, new species. 



Differing from A. papyraceus Fisher^ in lacking entirely the 

 actinolateral membrane, in having 13 marginal mouth spines form- 

 ing a sharply angular webbed series, the distal of conspicuous length, 

 and in having 9 rays. R = 225 mm., r = 52 mm., R = 4.3 r; 

 breadth of ray at base, 25 mm. Rays slightly swollen above base, 

 tapering to slender, flexible, pointed extremity; dorsal surface of ray 

 arched; that of disk flattened. 



The adambulacral armature, with the exception of the actino- 

 lateral membrane, is very similar to that of A. papyraceus, consisting 

 of 9 or 10 very delicate, webbed spines increasing in length from the 

 inner to the outermost, the outer two being longest and standing on 

 an extension of the next adorally situated plate (see figures of 

 A. papyraceus). In papyraceus the consecutive outer spines are 

 joined by a sort of actinolateral membrane, but in A. medusa they 

 are independent, the membrane being joined to the side of the ray 

 just above the base of the outer spine. 



The mouth spines form an angular series, the first to seventh 

 being on the actinostomial margin, the eighth on the angle of the 

 plate directed toward mouth of furrow, while the remaining five form 

 a group adjacent to the first adambulacral comb, on the very short 

 furrow margin of the plate. All are joined by membrane, and the 

 distal spines are of conspicuous length, though shorter than the 

 innermost. 



The abactinal spines are extremely delicate and resemble fine 

 glassy hairs. Eight or nine are borne on an eminence of the ex- 

 tremely thin plates and are united by membrane. The fascicles are 

 6 to 8 mm. long and spaced 2 or 3 mm. apart. 



Madreporic body slightly convex, 6 mm. in diameter, and situated 

 shghtly adcentral to the middle of r. The actinostome is wide 

 (38 mm.) and the tube-feet large, with large sucking disks. 



Type.— C&t. No. 32650, U.S.N.M. 



Type-locality. — Station 5605, Gulf of Tomini, Celebes, 647 fathoms, 

 bottom not recorded. 



The absence of an actinolateral membrane suggests the possibility 

 that in Myxaster the adambulacral armature may also be common 

 to two plates. In such an event this species would be placed in 

 Myxaster, and the actinolateral membrane might be retained as the 

 diagnostic character of Asthenactis. For the present it seems best 

 to classify this species in Asthenactis on the basis of the identity 

 of structure of the adambulacral plates. 



The name medusa is suggested by the twisted snake-like rays. 



' For description and figures, see Starfishes of the Hawaiian Islands, U. S. Fish Commission Bulletin 

 for 1903. Part 3, p. 1096, pi. 40, figs. 3, 3a. 



