REVISION OF PALEOZOIC STELLEBOIDEA. 



225 



Original description. " (Order Ophiuridse. Family Euryales.) 

 Body circular, covered with squamiform plates; genital openings 

 in the angles of junction of the arms beneath; arms (simple) formed 

 of alternating ossicula." 



Genoholotype. " Species Unica. Protaster sedgwickii. Forbes." 



Original description of P. sedgwickii. "The disk is circular, and 

 shaped like that of an OpTiiura. The arms are five in number, very 

 narrow, equidistant, and similar. 



"The upper and under surfaces of the disk were covered by small, 

 similar, more or less regular, polygonal or crescentic plates, imbri- 

 cated in scale-fashion, and having punctated surfaces. Those of 

 the under side of the 

 body are smaller and 

 more regular than 

 those of the upper. 

 The mouth is cen- 

 tral, and rather small 

 in proportion to the 

 disk. The buccal ap- 

 paratus is composed 

 of ten parts or proc- 

 esses, arranged in 

 pairs; half of each 

 springs from the 

 origin of each arm in 

 a diverging manner, 

 and meets the corre- 

 sponding half to form 

 a lanceolate tooth- 



1 i lr <* rkrrn'antirkn FlG> 22. ORAL SKELETON OF PAI^EUBA NEGLECTA, MUCH ENLARGED, 



u j t? i o II, AFTER JAEKEL> at AMB ULACBALIA; ad, ADAMBULACEALIA. 



deeply indenting the 



cavity of the mouth. Of how many separate ossicles each of the 

 buccal processes was composed the specimen affords but very indis- 

 tinct indication. They seem to affect a slightly falcate form at their 

 extremities. The arms were composed of alternating, somewhat 

 quadrate ossicula, the sides of which were deeply indented supe- 

 riorly, in order to form spiniferous crests. The spines were appar- 

 ently short, and not equal in length to the length of an ossicle, obtuse, 

 and few in a row. The under surfaces of the brachial ossicula were 

 not indented laterally. The central portions of the upper surfaces 

 of the brachial ossicles were hollowed out slightly, and the sutures 

 between them deeply impressed. About 12 of the brachial ossicles 

 were imbedded in the disk, and the parts of the dorsal surface of 

 the latter, corresponding to the arms and central skeleton, do not 

 present traces of scales, a feature seen in existing Euryales. 



