J20 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



Family BENTHOPECTINID^ Verrill, 1899, emended. 



Pararchastcrinsc Sladen, Challenger Aeteroidea, 1889, pp. xxviii, 4. 



Benthopcelinidx +Pontaslerinx Verrill, Trans. Conn. Acad., vol. 10, 1899, p. 217. 



A^otomijota Ludwig (CheirasUridx + Benthopectinidx), Sitzungsber. k. preuss. Akad. Wiss., 

 vol. 23, 1910, p. 4S5. 

 Phanerozonia with more, or less obviously alteniating, convex, spinifeious 

 marginal plates, an odd one above and below in the interradial angles of three 

 gene'ra; with small disk and long slender rays, and with the papulae confined to a 

 limited', often specialized, area at base of ray and adjacent portion of disk (or all 

 of disk and up to three-fifths of ray). Especially characterized by the presence 

 of a pair of muscle bands extending along the dorsal wall of the rays, from the 

 reo'ion of the third to eighth superomarginal plates to tip. Abactinal plates with- 

 out definite arrangement, either simple and flattened, with one or few spinelets, or 

 in the form of low paxilla?, both kinds sometimes occurring in the same species. 

 Adambulacral plates with a salient inner angle bearing a series of spinelets; one 

 to several conspicuous actinal (or subambulacral) spines. Actinal intermediate 

 plates few and interradial areas small. Pedicellarite when present pectinate, fas- 

 cicular, or rarely bivalvate. Anus present. Xo superambulacral plates. Tube 

 feet with sucldng disks. Intestinal coecum thick.saccular, four-parted. 



KEY TO THE KNOWN GENERA OF BENTHOPECTIXID.E. 



a'. No unpaired interradial marginal plates; dorsal muscle bands Bometimes attached to proximal 

 ambulacral ossicles by a tendon. 

 b'. Paxilla: with numerous spinelets or granules. 

 c'. Papularia not two-lobed, usually more or less distended. 

 d'. Pedicellariae when present two-jawed and occurring on the adambulacral plates; the latter 



with two spines on their surface Pontaster Sladen. 



rf*. Pedicellarise fasciculate, occurring on dorsal, marginal, and actinal intermediate plates. 



Peclinaster Perrier, p. 122. 

 c'. Papularia not swollen, more or less distinctly two-lobed. 

 d'. Pedicellariae usually present and pectinate; actinal intermediate plates always present on 

 disk; no tuft of rather long paxillar spinelets near first superomarginal. 

 e'. Dorsal muscle bands not unusually large and not attached to enlarged crest of a proximal 

 ambulacral ossicle; adambulacral plates with one enlarged subambulacral spine. 



Cheiraster Studer. 



«'. Dorsal muscle bands large and attached by a prominent tendon to a specialized knob or crest 



of either one or two proximal ambulacral ossicles, as well as to adjacent superomarginal 



plates; adambulacral plates with two or more enlarged subambulacral spines; marginals 



very spiny Luidiaster Studer, p. 127. 



<P. With a tuft of rather long paxillar spinelets near the first superomarginal plate; primary plates 

 of disk each with one large spine; pedicellarise unknown; adambulacral plates with two 

 subambulacral spines; actinal intermediate plates absent; innermost marginal mouth spine 



not prolonged MarcelasUr Koehler. 



6'. Paxillse with usually but one spinelet, that on the primary plates of disk becoming a largo spine; 



papularia flat, two-lobed; no pedicellariae Gaussastcr Ludwig. 



a'. Odd interradial marginal plate present in some- or all of the interradii. Dorsal muscle bands not 

 attached to a proximal ambulacral ossicle. 



