370 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



KEY TO THE KNOWN SPECIES OF PTEBASTER — Continued. 



p. R=1.4 r; suboral Bpines very slender and long, without, trace of three-sided tip; no 

 heavy eupradorsal reticulations; oral spines six; spiracles exceedingly numerous. 



coscinopeplus Fisher, 

 c^. Actinolateral membrane very narrow, not defining ambitus; actinolateral spines of approxi- 

 mately equal length except at very tip of ray; no supradorsal reticulations; first two 



oral spines very flat and truncate obesus Clark. 



c'. Adambulacral armature three to five spines, 

 rf". Oral spines three to five, not united by a web. 



«'. Adambulacral spines short, scarcely projecting beyond web stellifer Sladen. 



«'. Adambulacral spines slender, projecting far beyond web danx Verrill. 



€p. Oral spines united wholly, or in groups, by a web. 

 «'. Oral spines of each mouth angle all united by a common membrane. 

 /". Actinolateral membrane fairly broad, or very broad, the lateral fringe defining ambitus. 

 g'. Suboral spine three-edged, sharp; apertures unusually large; adambulacral spines 



five; oral spines five; R=L3+r temnochiton Fisher. 



ff'. Suboral spine not three-edged; apertures not unusually large; adambulacral spines 

 three to five. 

 A'. Adambulacral spines usually three, sometimes four, short, scarcely projecting beyond 



web; R=1.4-f r rugatus Sladen. 



h''. Adambulacral spines three to five, usually four, projecting far beyond web. 

 i'. R=1.75r±; dorsal membrane thin, evidently TeticuliLted..semireticulatus Sladen. 



■P. R=1.4 r±; dorsal membrane thick, not at all reticulate ingolfi Perrier. 



p. Actinolateral membrane narrow not defining ambitus; actinolateral spines short, little 

 longer than outermost adambulacral spine; oral spines six; adambulacral spines five; 



spiracula very abundant; R = 1.6 r multiporus Clark. 



e'. Oral spines webbed so as to form at each mouth angle four groups; two innermost spines 

 long, four lateral short, each group united by web; adambulacral spines usually four; 



no spiracula alveolatMs Perrier. 



6'. Rays regularly six, seven, eight, or nine, usually six; supradorsal membrane thick; spiracula 

 numerous; abactinal stirface spiny; actinolateral membrane and furrow webs thick; adambula- 

 cral spines four to seven; oral spines five or six, completely webbed; R=1.4 to 1.65 r. 



obscurus Perrier. 



Genus DIPLOPTERASTER Verrill. 



Diplopteraster Yerrill, Amer. Journ. Sci., vol. 20, 1880, p. 400. Type, Pteraster multipes Sara. 

 Retaster Sladen, part. Challenger Asteroidea, 1889, p. 477. 



Diagnosis. — Pterasteridse agreeing with Retaster in having a strongly reticu- 

 lated supradorsal membrane, but differing in having two kinds of adambulacral 

 plates, less prominent alternating with more prominent, and correlated with them, 

 two sorts of furrow combs, one larger and set farther into furrow, and having some- 

 times one spine more, the other set back slightlj'; tube feet in four rows; mouth 

 spines all webbetl together; actinolateral membrane (in contrast to Retaster) very 

 broad, and fleshv in fully adult specimens. Madrei)oric body not bearing a tuft of 

 spines on its summit." 



Three closely related species are known: besides the type, Diplo pteraster 

 verrucosus (Sladen), Atlantic entrance to Strait of Magellan, and D. peregrinatnr 

 (Sladen), off Cumberland Bay, Kerguelen Island. 



« I am not certain as to the value of this character. Retaster and some, but apparently not all, speciee 

 of Pteraster have a paxilla on the madreporic body. 



