MONOGRAPH OF JAPANESF- OPHIUKOIDEA. 7 



Key to families of Phvijnophiurida. 



A — Kadial shields very rudimentaiy or more or less long und bar-like ; 

 arms not exceedingly long, always simple ; lateral arm plates sub- 

 ventral in position ; arm spines not confined to the ventral side of 

 the arm ; vertebrae rather slender, not exceedingly short and dis- 

 coidal ; vertebral articulation either zygospondyline or streptospon- 

 dyline ; both upper and lower muscular fossae of the vertebrae 



large OpTdomyxidœ. 



A A — Kadial shields very long and bar-like ; arms exceedingly long, either 

 simple or branched ; lateral arm plates ventral in position ; arm 

 spines confined to the ventral side, all serving as tentacle scales ; 

 vertebrae very stout, exceedingly short and discoidal ; vertebral arti- 

 culation typically streptospondyline ; upper muscular fossae of the 

 vertebrae extremely large, the lower very small. 



a — Teeth very stout, arranged in a single vertical row ; oral and dental 

 papiUae not very well developed ; adorai shields very stout ; arms 

 not annulated by rows of hook-bearing granules ; arm spines covered 



by thick skin Trichastendœ. 



aa — Teeth and dental papillae, often also oral papillae, all similar, 

 spiniform ; adorai shields not very stout ; arms annulated by double 

 rows of hook-bearing granules ; arm spines naked or covered by 

 very thin skin GorgonocepJiàlidœ. 



Family 1. Ophiomyxidae (Ljungman, 1866) mihi, 1915. 



Disk and arms covered by a soft skin. Radial shields very 

 rudimentary or more or less long and bar-like. The radial shield 

 and genital plate articulate with each other by a simple face. 

 Genital scales slender, bar-like, articulated with the genital plate 

 at a distance inw^ards from the outer end of the latter. Peristomial 

 plates very large, either double or triple, and thin or entire and 



