276 THE STELLERO1DEA 



regarded as an ally of Euryale, but some authors have urged its removal 

 to the Asteroidea, ascribing a dorsal position to the madreporite. It is 

 no doubt in external appearance more like the Cladophiurae than the 

 Streptophiurae, but the external resemblance to Eiiryale is probably due 

 to homoplastic modifications. 



FAMILY 6. THE LIVING STREPTOPHIURAE. No attempt has yet been 

 made to arrange the living Streptophiurae into families, and this cannot be 

 done with advantage without further knowledge about several points. Some 

 of the most remarkable genera are known only by single specimens, 

 which are very small and probably immature. Ophiohelus and Ophwthotia 

 present a certain resemblance to the Lysophiurae in the structure of the 

 ambulacral ossicles. Ophioyeron, with its long, rod-shaped, ambulacral 

 ossicles lying in opposite pairs, is much like Ophiurina, but the evidence 

 available at present is insufficient to justify its inclusion in the Ophiuri- 

 nidae. Hence it is advisable at present to leave the living Streptophiurae 

 arranged according to Bell's scheme (3). When the classification is 

 attempted, probably Ophioteresis will form one family, and Ophiosciasma 

 another ; Hemieuryale, Sigsbeia, Ophiochondrus, and Ophiomyccs may con- 

 stitute a third. 



A. No under arm-plates Ophioteresis, Bell. 



B. Under arm-plates imperfect Ophiosciasma, Lym. 



C. Under arm-plates moderate or well developed. 



a. No upper arm-plates I. No radial shield Neoplax ; Ophiohelus, 

 Lym. ; Ophiotholia, Lym. (?). II. Radial shields present 

 Ophioscolex, Mull. & Trosch. ; Ophiambix, Lym. ; Ophiogeron, 

 Lym. ; Ophiobyrsa, Lym. ; Ophiomyxa (pars), Mull. & Trosch. 



/?. Upper arm-plates minute or formed of scattered plates Ophio- 

 myxa (pars), Miill. & Trosch. ; Ophiomyces, Lym. ; Ophiochondrus, 

 Lym. ; Hemieuryale, Martens ; Sigsbeia, Lym. 



ORDER 3. Cladophiurae, Bell (1892). 



Ophiuroidea in which the vertebral ossicles articulate with one another 

 by means of hour-glass-shaped surfaces (Fig. XXXIII.), and are covered 

 by granular deposits in the thick integument. The arms may be simple 

 or branched repeatedly. 



FAMILY 1. ASTRONYCIDAE. Cladophiurae with simple unbranched 

 arms. GROUP 1. With large disc Astrotoma, Lym.; Astromyx, Miill. 

 & Trosch. ; Astrochele, Verr. GROUP 2. Disc of medium size Astrogomphus, 

 Lym. ; Astroporpa, Oersted & Liitken. GROUP 3. Disc small Ophiocreas, 

 Lym. ; Astroschema, Oerst. & Lutk. ; Astroceras, Lym. FAMILY 2. 

 TRICHASTERIDAE. Cladophiurae with arms branching a few times near 

 their free ends. Genera, recent Trichaster, L. Ag. ; Astroclon, Lym. ; 

 Astrocnida, Lym. Fossil Astrocnida, Lym. FAMILY 3. GORGOXOCEPHA- 

 LIDAE. Cladophiurae with arms branching much and from their base. 

 Euryale, Lam. ; Gorgonoceplialus, Lym. ; Astrophyton, Ag. (Fig. XXXII.) 

 Ophiocrene, Bell. 



