MONOGRAPH OF JAPANESE OPHIUROIDEA. 



319 



Fig. 8S. Ophifirachna incrassatn. xl^. '(. From above, h. From below, c. 

 Skle view of four arm joints near disk, showing the regenerated arm spines. 



accessory oral shields are very rudimentary or absent.'^ Compar- 

 ing these fom- specimens, we find that the arm spines are longer, 

 blunter and more flattened in the larger specimens. The propor- 

 tion of width to length of the oral shields is not constant. The 

 size ratio of the accessory oral shield to the oral shield proper 

 differs in specimens. The pairs of the adorai shields are sometimes 

 asymmetrical. The arm spines may regenerate. 



Key to Japanese genera of Ophioderniatinœ. 



y^^ Single oval tentacle scale to each pore ; three or four arm spines ; 



radial shields partly naked Bathypectinura. 



./i^— Two tentacle scales, of which the abradial one overlaps the base 

 of the loAvest arm spine ; six or more arm spines. 



a — Radial shields covered over Pectinura. 



aa — Radial shields naked OpJdaraclinélla. 



1) lu Pectinura, Ophiarachnella, Bathypectinura and Ophiarachna, the accessory oral shields 

 are not constantly present. I therefore consider it more natural to refer Ophiopeza dnnhyi 

 FABQrHAR to Ophiarachna than to I'ect'mnra, notwithstanding the absence of the accessory oral 

 shields. 



