CLASS II 



OPHIUROIDEA 



255 





and-socJcet joints. The arm-plates are more or less completely developed and the side 

 arm-plates may carry spines. Arms may he very short with relatively enormous 

 tuhe-feet, as is apparently the case in Eudadia. 



This Order includes a number of Paleozoic forms and not a few Recent 

 species. Important genera are Ophiurina Stürtz, Devonian, with separate am- 

 bulacral ossicles and no ventral arm- ^ 



plates; Lapworthura Gregory, Silurian, 

 with barely fused ambulacral ossicles, 

 and no ventral arm-plates ; Sympterura 

 Bather, Devonian, similar to Lap- 

 worthura, but with narrower rays and 

 spinulose disk ; and Eoluidia Stürtz, 

 Devonian, with fused ossicles, and with 

 ventral arm-plates. The genus Ony- 

 chaster Meek and Worthen (Fig. 361), 

 Lower Carboniferous, has usually been 

 regarded as representative of the 



mndprn Enrvalid«? hnt thp oharaofpr ni OnychasterßexiUsM. and W. Lower Carboniferous ; 

 moaern JLUryaiiaS, DUÜ tne Cnaracter OI Crawfordsville,Ind.(after Meek and Worthen). ^,In- 

 the ambulacral ossicles necessitates itS dividual of the natural slze with rolled up anns ; 

 , . . - . , ^, 111 ^'^^ dorsal covering of the central disk is removed, 



incmSIOn m tniS Order. ine remarkable exposin^ the mouth frame. B, Mouth frame enlarged, 



Silurian genera Eudadia Wood ward, and ""'"'''^ ''"'" "^"^'^ ' ^^' '''''^''^"' ''''''''' ^"^"^«^• 

 Euthemon Sollas, are exceedingly difficult to place, and their relation to other 

 Ophiurans is problematical. 



Fig. 361. 



Order 3. CLADOPHIUROIDA. 



Ophiuroidea in ivhich the vertebral ossides are complete and articulafe with each 

 other hy means of hoiirglass-shaped surfaces. The arms are oflen dichotomously 

 branched and lack regulär series of arm-plates. 



This Order includes a large number of Recent forms, those with branched 



FiQ. 362. 

 Aspidura loricata (Goldfuss). Muschelkalk ; Waschbach, Würtemberg 

 natural size (after Quenstedt). 



A, ßroup of individuals of the 

 B, Ventral aspoct, enlarged (after Pohlig). 



arms (Astrophyton, Gorgonocephalus, Euryale) being known as " Basket-fish " or 

 " Sea-spiders." Fossil forms are rare, but certain Mesozoic remains of doubt- 

 ful Position have been referred to the Recent genera Astrocnida and Euryale. 

 Onychaster, the Streptophiuran referred to above, has peculiarities that suggest 



