252 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



(P. Abactinal skeleton formed of plates disposed in longitudinal and transverse series fonning 



an irretnilar or regular mesh work, more or less open, the plates bearing isolated spines 



or groups of epinelets, but never fans of epinelets. 



e'. AmpuUse single; no pediccllarise; interbrachial septa weak, more or less rudimentary; 



abactinal reticulated skeleton irregular, bearing single spinelets, or groups of spinelets, 



or larger spines Echinasteridse, p. 258. 



e". Ampulte double. 

 /'. No pediccUaria;; disk very small; no interbrachial septa; skeletal reticulations roughly 

 in the form of triangles grouped in hexagons; skin, and the large obtuse spines beset 



with rough scales or spinelets Mithrodiidx." 



p. Small two-jawed upright, or largo low bivalved pedicellari«; disk large, interbrachial 



partitions well developed, with plates; no superficial covering of scales or spinelets over 



the skin and spines. 



^'. Rays numerous; numerous madreporic bodies; pedicellarise consisting of two upright 



tapering jaws arising from a small independent plate; no calcareous rosette in suckers 



of tube feet; skeleton open reticulate, armed with large isolated spines covered 



with membrane beset with calcareous granules Acanthaslerxdxfi 



g^. Rays five; one madreporic body; large low bivalved pedicellariae on superomarginal 

 plates, in addition to a few very small upright two-jawed pedicellariae on the abactinal 

 surface and adambulacral plates; a calcareous reticulum forming a rosette in suckers 

 of tube feet; abactinal plates regularly arranged, leaving small triangular papular 

 spaces, and bearing small isolated spines; actinal intermediate plates bearing one 



to several large, flat, spinelets Valvasteridx. c 



c?. Abactinal skeleton entirely aborted, only the ambulacral and adambulacral systems remaining- 



Intogument covered with small membrane-enveloped spines Cn/asieridx.^ 



a^. Mouth plates large and shaped like a pointed spade or like a plowshare, with conspicuous marginal 

 and usually also suboral spines; furrows wide, adambulacral armature pectinate. 

 6'. Marginal plates paxilliform, in either one or two series; abactinal paxillse never with long spine- 

 lets united by membrane but fascicular or penicillate; mouth plates spade-shaped. Actinal 

 intermediate plates present; adambulacral armature in two series at right angles; interbrachial 



septa Solasteridx, p. 305. 



6^. Marginal plates either hidden by a supradorsal membrane, or if visible not conspicuous and 

 paxilliform; abactinal plates with spines more or less united by membrane; mouth plates 

 plowshare-shaped (of the type of Pteraster) ; actinal intermediate plates absent or indistinguish- 

 able; adambulacral armature in one or two series; interbrachial septa present or rudimentary. 

 C*. No supra<l(irs;il membrane forming a special nidamental cavity; no segmental pores or papilla;. 

 (p. Interbrachial septa partly calcified; adambulacral armature forming with that of inferomar- 

 ginal plate a single transverse series, never webbed; abactinal skeleton composed of round- 

 ish plates, or lobed plates forming a wide mesh Korethrasteridx, p. 340. 



" Mithrodiina Viguier, 1879, p. 128; Mithrodina; Perrier, 1884, p. 164; Mithrodidae Perrier, 1894, 

 p. 4; Mithrodiida; Fisher, 1906, p. 1094. This family contains only one genus, Mithrodia Gray, and 

 differs from the EchinasteridEe in having double ampulla?, in lacking interbrachial septa, and in having 

 the entire body, including spines, overlaid with rough granules and squamitorm tubercles or spinelets. 



^ This is equivalent to the Acanthasterinee Sladen, 1889. Acanlhaster is a very isolated type, the 

 sole survivor of perhaps a once extensive group. The family of which it is the type differs from the 

 Echinasteridas, restricted, in having double ampullae, well developed interbrachial septa, numerous 

 madreporic bodies, upright, two-jawed pedicellariae, and many rays. 



c This family is equivalent to the Valvasterinae Viguier, 1878. It differs from the Echinasteridae 

 in having double ampullae, bivalved and two-jawed upright pedicellariae, a regular abactinal skeleton, 

 conspicuous marginals, strong interbrachial septa, and a rosette of calcareous reticulum in the suckers 

 of the tube feet. Kcehler also considers this group of family rank ("Valvast^rides," Koehler, 1910, 

 p. 176). 



^"Cryaatdrid^es" Koehler, Expedition antarctique franfaise, Echinodermes, Dec, 1906, p. 24, 

 Genera Cryastar Koehler and Magdaknaster Ktehler. 



