MOXOGKAPH OF JAPANESE OPHIUROIDEA. 283 



Key to Japanese genera of OpMolejndinœ, 



A — Tentacle pores limited to a few basal arm joints ; disk plates or 

 scales, as well as radial shields, more or less intimately soldered 

 together; oral papillae more or less soldered together to form a 

 single x>iece ; arm joints long and hom'-glass-shaped ; dorsal and 

 ventral arm plates more or less rudimentary ; arm spines very 



minute and peg-like Ophiomnsium. 



AA — Tentacle pores well developed throughout the entire length of the 

 arm ; disk plates or scales imbricating ; oral papillae not soldered 

 together ; arm joints not very long ; dorsal and ventral arm plates 

 usually well developed ; arm spines not very minute. 



a — No true tentacle scales, though the lower arm spines may some- 

 times serve as one ; disk covered with fine, granule-like scales ; 

 genital shts very minute, placed at the inner corners of the inter- 

 brachial ventral surfaces ; dorsal arm plates more or less widely 

 separated from one another by supplementary plates or naked 

 spaces ; ventral arm plates separated from one another at least in 



the basal arm joints Ophiopenia. 



aa — Tentacle scales always well developed. 



b — Dorsal arm plates entire, without supplementary plates ; ventral 

 arm plates rhomboidal and separated from one another except at 

 the arm base ; lateral arm plates of either side meeting both above 

 and below except at the arm base ; disk covered with large plates 

 and smaller scales ; radial shields very stout ; one or two tentacle 



scales Opliiozonella. 



bh — Dorsal arm plates not entire, accompanied by supplementary plates ; 

 ventral arm plates quadrangular, widely in contact with one another ; 

 lateral arm plates of either side not meeting above or below. 



c — Dorsal arm plates proper not divided, accompanied by small sup- 

 plementary plates on both sides or also along the outer border ; 

 disk covered with two kinds of scales, the larger ones surrounded 

 by a zone of smaller ones ; radial shields moderately stout ; two 

 tentacle scales, together forming an oval OpJdolepis. 



