MONOGRAPH OF JAPANESE OPHIUEOIDEA. 107 



In my opinion, the shape of the radial shields is an important 

 character in the systematic of the present family. The radial 

 shields of the genuine Opldacantha are long, narrow and bar-like. 

 In Yeerill's key, the species of OpMophtlialmus would appear as 

 belonging to Ophialcœa, but the latter is a close ally of Ophiaccwtlia, 

 with long and bar-like radial shields. 



Key to Japanese species of OpMo2:)Mhahniis. 



A — Disk beset with some granules, or sometimes with spines ; a single 



large tentacle scale to each pore. 

 a — Disk with granules only, without spines. 

 h — Disk granules abundant, uniformly distributed on both the dorsal 



and ventral sides, 

 c— Kadial shields small, widely separated from each other; several 



granules occur at the outer border of the dorsal arm plates of basal 



free arm joints ; fom* or five oral papillae, of which tlie outermost 



one arises from the first ventral arm plate. 

 d — Disk scales coarse ; outer second oral papilla very large, "s^'ide ; six 



or seven arm spines cataUimmoidus. 



dd — Disk scales fine ; innermost oral papilla largest ; four arm spines . . 



normani. 



cc — Radial shields large, lying closely side by side in pairs, but not in 



contact with each other ; six oral papillae on either side ; eight or 



nine arm spines . . , , leucorhahdotus. 



bh — Disk granules few, being present only in the central parts of the 



dorsal surface, radial shields large, widely separated from each 



other ; three oral papillae on either side ; eight arm spines 



, codonomorpha. 



aa — Disk beset Avitli stout rough spines, besides granules ; radial shields 



moderately large ; four oral papillae on either side ; eight arm 



spines liylacantlia. 



AA — Disk beset with many stumpy tubercles with stelhform crowns ; radial 



