78 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



TAKSASTER ALASKANUS, new species 



Plate 30, Figures 4, ia-id; Plate 36, Figure 3; Plate 37, Figure 4 



Diagnosis.— Rays 5, slender, subterete, tapering gradually from a swollen base to a 

 subacute tip; disk small marked off by a distinct constriction from ray; interbrachial 

 angle sharp, closed; carinal plates forming a slight convex ridge; spinelets small, 

 uniform, several to a plate, arranged (with numerous crossed pedicellariae) in trans- 

 verse bands, between which are narrow transversely oriented papular areas; infero- 

 marginal plates with two spines the upper uniform with the general spinulation, the 

 lower enlarged, subclavate, obtuse, about 2 mm. long; adambulacral plates dipla- 

 canthid, except 8 or 10 proximal triplacanthid plates; oral plates with five spines, of 

 which two stand on actinostomial margin; straight pedicellariae, small, broadly 

 lanceolate, confined to oral and adambulacral plates; tube-feet proximally four- 

 ranked distally biserial. Differing from T. galapagensis (Ludwig) in having several 

 mobile spinelets on the abactinal plates; subterete, clavate, blunt major infero- 

 marginal spines (instead of almond-shaped ones); five instead of two oral spines; and 

 no straight pedicellariae on the abactinal and marginal plates. R 67 mm. ; r 6.5 mm.; 

 R = 10 r; breadth of ray at base, 8 mm.; at widest part, 12 mm. 



Description. — The skin is relatively thick and completely obscures the outlines 

 of the plates, which, however, are slightly indicated by shallow transverse depressions 

 denoting the papular areas. The carinal plates form a rather broad, slightly convex 

 ridge. The numerous small, slightly tapered, thorny tipped spinelets (about 0.8 to 

 1. mm. in length) are arranged in somewhat irregular consecutive transverse bands 

 or ranks, which are separated by the transverse depressions noted above. The 

 spinelets of the abactinal and superomarginal plates have the appearance of being 

 of nearly uniform size, blunt, upward of three or four to a plate, and accompanied 

 by numerous crossed pedicellariae, which, being largely absent from the papular 

 areas, accentuate the transverse arrangement of the spinelets. The superomarginal 

 plates are set off by a very slight longitudinal furrow on their upper margin and each 

 plate carries about three spinelets in a vertical series, the consecutive series being 

 rather close on account of the considerable overlapping of the plates. 



The inferomarginal plates which closely join the adambulacral series (without 

 any actinal plates between) carry usually two spines in a transverse series. The 

 inner is heavy, clavate, blunt, about 2 mm. long, and situated close to the outer 

 adambulacral spine. Occasionally two subequal slightly smaller spines take the 

 place of the larger inner spine. The second spine is about half as long, much slenderer, 

 and is similar to the lower superomarginal spinelet from which it is spaced a little 

 more than its own length. This outer spinelet forms a longitudinal series separated 

 from the superomarginals by a slight furrow and is in no other way differentiated 

 from the general spinulation. The inner enlarged spine forms a prominent longiseries 

 just external to the bristling adambulacral spines. On a number of plates a second 

 accessory spinelet makes its appearance. 



The skeleton is characterized by more compactness than that of other species, 

 the skeletal meshes being smaller and the plates, especially the dorsolaterals, larger. 

 The marginal plates are very firmly imbricated, the superomarginals being four-lobed, 

 while in the inferomarginals, the ventral, or adambulacral, lobe is pretty much sup- 

 pressed. The carinals are four-lobed and very firmly imbricated. The dorsolaterals 



