58 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



6 J . Actinal plates present; crossed pedicellariae with the numerous terminal teeth uniformly 

 tiny; gonads opening ventrally; actinal plates in one or two longiseries; prominent 

 unguiculate straight pedicellariae in some species Anteliaster Fisher. 



b*. Actinal plates absent, the inferomarginals juxtaposed to the adambulacrals; inferomarginal 

 spinelets small; crossed pedicellariae all of one kind, small, with numerous small uniform 

 terminal teeth; gonads opening on extreme edge of abactinal area — Hydraslerias Sladen. 

 a 3 . External to the adambulacral spines is a longitudinal series of prominent inferomarginal spines 

 conspicuously larger than the superomarginals (which are subequal to the abactinal spine- 

 lets) ; no actinal plates; a quartet of strong interbrachial marginal plates; first pair of 

 postoral adambulacral plates narrowly separated or touching by the adoral corners. 



6'. Straight pedicellariae not unguiculate nor broadly spatulate; an accessory inferomarginal 

 spinelet above the major spine (at least proximally); adambulacral plates diplacanthid or 

 diplacanthid and monacanthid; interbrachial marginals not much enlarged; supero- 

 marginals regularly four-lobed (not warped or irregular, nor three-lobed) . . Tarsaster Sladen. 



b 2 . Straight pedicellariae unguiculate, often also strongly spatulate; no accessory inferomarginal 

 spinelet or tubercle; adambulacral plates predominantly monacanthid (a few plates may be 

 diplacanthid); two enlarged interbrachial superomarginals overlap two corresponding, 

 sometimes enlarged inferomarginals; superomarginals often three-lobed or irregularly four- 

 lobed (proximal plates generally fairly regular) Ampheraster Fisher. 



Genus PEDICELLASTER Sars 



Pedicellasler Sabs, Oversigt af Norges Echinodermer, Christinania, 1861, p. 77. Type P. 

 typicus Sars. — Fisher, 1923, p. 251. 



Diagnosis. — Crossed pedicellariae of two kinds: larger, with slender jaws having 

 usually four curved prominent terminal teeth, and below these on the slender shank, 

 one to five slender thornlike teeth; the smaller pedicellariae of the usual Asteriid 

 type; actinal plates well developed, in transverse series, the number of plates in series 

 in the adults of some species increasing toward the middle third of ray and decreasing 

 in the distal third; young specimens with one or two longitudinal series; skeleton of the 

 quadrate-mesh type, often delicate, of +-and Y-form plates, the intervals medium 

 sized to large; dorsolateral skeleton irregular; spinelets small, the inferomarginal not 

 conspicuously larger than the rest; the first postoral pair of adambulacral plates 

 widely separated interradially; furrow narrow, tube-feet biserial; gonads normally 

 opening laterally at a slight distance from disk. 



Remarks. — The characteristic structure of the actinal skeleton is not attained 

 until specimens have reached some size. It is, however, fundamentally different from 

 that in large examples of Anteliaster, where the actinal plates are in one or two simple 

 longiseries, the outer extending farther long the ray than the inner. Young Pedicel- 

 laster passes through this stage, and, so far as the actinal plates are concerned, is then 

 not different from Anteliaster. Later, in magister, megalabis, and orientalis, additional 

 plates are added more numerously in the middle third of the ray than at either the 

 base or distal portion, and the arrangement in longiseries is consequently lost. The 

 plates become closely imbricated in transverse series, and the transverse series tend 

 to become less well connected with their neighbors. 



Young examples of Pedicellaster may be recognized by the presence of two sorts 

 of crossed pedicellariae, of which the larger, ventral, sort have slenderer jaws with 

 only four terminal teeth. None of the other nearly related genera have this type of 

 pedicellaria, the terminal teeth in all cases being uniformly small and the jaws rela- 

 tively shorter and stouter. 



