218 ART. 2. — H. MATSÜMOTO : 



Key to Japanese species of Ophiothrix, 



A — Dorsal arm plates more or loss rhomboidal, not very wide, only 

 slightly wider than long or longer than wide, only slightly in con- 

 tact with one another. 

 a — Ventral arm plates notched outwards. 



h — Arms short, less tlian five times as long as the disk diameter. 

 c — Kadial shields entirely or mostly naked. 



d — First dorsal arm plate with a tubercle, on which a conspicuous 

 spine is borne ; disk closely beset with spines, which are cylindrical, 



blunt and rough at tip panchyendyta. 



dd — First dorsal arm plate free of tubercles and spines ; disk beset with 

 trifid, or rarely bifid, tubercles or thorny spines of various length 



or with both Icoreana. 



. cc — Kadial shields, as well as disk, closely beset with stout, thorny 



spines of almost uniform length marenzeUeri. 



hh — Arms long, twelve to fifteen times as long as the disk diameter ; 

 radial shields covered by a thick skin, except at the outer adradial 

 border, where the}^ are naked ; disk beset on the dorsal side with 



slender, thorn}^ spines of various length macrobraclda. 



aa — Ventral arm plates with entire and convex outer border ; arms four 

 to seven times as long as the disk diameter, 

 e — Radial shields naked ; disk beset with bifid or trifid tubercles and 



thorny spines eusteiixi. 



ee — Radial shields, as well as disk, closely beset with stellate tubercles 



and thorny spines stabilis. 



A A — Dorsal arm plates more or less fan-shaped, very wide, much wider 

 than long, widely in contact with one another. 

 / — Dorsal side of disk entirely free of spines ol* tubercles, or beset 

 with a group of thorny tubercles only at the central region, with a 

 beautiful network of white streaks; each doi-sal arlxi; plate with a 

 transverse white streak ; arms about fifteen times as long as the 

 disk diameter , . . ..,. . ..,.,,.. nereidina. 



