MONOGIÎArH OF JAPANESE OPHIUROIDEA. 217 



slender transverse and stout longitudinal bars ; those beyond Y- 

 shaped. The internal structures of Ophiothrix koreana Duncan are 

 alnaost similar to those of the preceding, but the peristoraial plates 

 are distinctly larger, the genital plates are shorter and firmly fixed 

 only to the third and fourth vertebrae, and the genital scales are 

 much smaller. In Ophiothela dance Veerill, the oral frames are 

 less stout than in Ophiothrix nereicUna and 0. koreana, but have 

 also well developed lateral wings with wavy peripheries. The 

 peristomial plates are small and oval and have a conspicuous notch 

 at the middle of the outer border. The genital plates are firmly 

 fixed to the first to third or fourth vertebras, and have also a 

 conspicuous ball -like articular condyle near the outer end ; the 

 muscle impression just anterior to the articular condyle is not very 

 distinctly differentiated. The genital scales are also short, wide, 

 flat and leaf-like. The dorsal side of the first vertebra is like a 

 cross, with very slender transverse and stout longitudinal bars ; 

 and of those beyond Y-shaped. Judging from Lyman's statements, 

 Ophioma^a, Ophiocnemis, Opliiopsammium and Ophiogymna do not 

 appear to differ fundamentally in their internal structures from the 

 forms here described. 



Key to Japanese genera of Ophlotrichidœ, 



A — Dorsiil arm plates entire, 



a — ^Disk beset with spines or stumpy tubercles ; arm spines long, 



flattened, serrate, hyaline Ophiothrix. 



aa — Disk entirely free of spines or tubercles ; arm spines of moderate 



length, conical, entire, opaque Ophiomaza. 



AA — Dorsal arm plates repl'esented by a number of nodule-like granules 

 or secondary plates ; disk beset with granules or tubercles ; arm 

 spines of modtrate length, conical, serrate, hyaline Ophiothela. 



