490 BULLETIN lOO, UNITED STATES NATIONAL MUSEUM. 



Genus TARSASTER Sladen. 



Tarsaster Sladen, 1889, p. 439. Type, T. stoichodes Sladen. 

 TARSASTER DISTICHOPUS Fisher. 



Plate 141, fig. 1 ; plate 155 ,figs. 3, Sa-c. 

 Tarsaster distichopus Fisher, IQllb, p. 92. 



Diagnosis. — Rays 5. R=48 mm., r=5 mm., R=9.6 r; breadth of 

 ray at base 6.5 mm. Disk very small, convex; rays long, slender, 

 bluntly pointed; abactinal surface prominently arched, with a very 

 slight midradial carinal ridge; actinal surface nearly plane, the sides 

 of ray as defined by the 2 series of marginals, nearly perpendicular, 

 but sloping inward toward the furrow, slightly. Differing from 

 Tarsaster stoichodes Sladen in having 1 adambulacral spine, 1 spine 

 on the midradial plates, prominent, unguiculate forficiform pedicel- 

 lariae in the furrow, and biserial tube feet. 



Description. — Plates arranged as follows: a carinal, a supero- 

 marginal, and an inferomarginal regular longitudinal series of 

 4-lobed, strongly imbricating plates, the transverse lobes nearly 

 obsolete on the inferomarginals, which are contiguous to the ndam- 

 bulacrals (no actinal intermediate plates present). Between the 

 carinal series and the superomarginals, for the proximal half of the 

 ray, there are 2 not very regular series of smaller 4-lobed and 

 3-lobed plates, which on the distal half of the arm are reduced 

 to a single series. These plates imbricate directly with one another 

 in a longitudinal direction, as in the case of the carinals and margi- 

 nals, but laterally they join the superomarginals on the one hand 

 and the carinals on the other by one or, sometimes proximally, by 

 two elliptical secondary ossicles, as shown, perhaps, better in the 

 figure than by description. There are thus proximally 3 dorsolateral 

 series of papular areas and distally 2, containing 1 or 2 papulae, 

 while there is, in addition, on each side, an intermarginal series of 

 smaller areas with 1 papula to an area. The small disk is composed 

 chiefly of primary apical plates, not very regularly arranged, with 

 1 or 2 papulae in the intervening areas. 



The carinal plates, the dorsolaterals, the superomarginals, and the 

 secondary elliptical, or smaller connecting, plates each bear a short 

 conical spine on a central boss of the plate, those of the dorsolaterals 

 and secondary ossicles being one-half to two-thirds the size of the 

 other spines, which are 1.25 to 1.5 mm. long. The inferomarginals 

 (except the first plate) have each a stouter spine 2 mm. long, the 

 series standing on the actinolateral margin of the ray. Each plate 

 also carries, scattered over its surface, 3 to as many as G or 8 con- 

 spicuous, ovoid (as seen from side) forcipiform pedicellariae, usually 

 about 0.45 mm. long. They give the appearance of an open, rather 



