MONOGRArn OF JAPANESE OPHIUROIDEA. 



15 



O <r 



five oral papillae 

 on either side of 

 each jaw, trian- 

 gular, with acute 

 apices, the proxi- 

 mal parts being 

 covered by a com- 

 mon skin. Teeth 

 stout, triangular, 

 acute. 



Six arms, of 

 w]iich three are 

 longer than the 

 otlier three, as a 

 result of schizo- 

 gony and regene- 

 ration ; very 

 slender, only hori- 

 zontally flexible. 

 Outer vertebrae 

 divided into bar- 



hke halves by a longitudinal fusiform pore. Dorsal arm plates 

 entirely absent ; and the dorsal side of the vertebra) are seen 

 through the skin to be rhomboidal, long and narrow. Lateral arm 

 plates low, subventral in position ; those of both sides meetin<^ 

 each other below, but widely separated above. First ventral arm 

 plate very small, rhomboidal, with the inner sides longer than the 

 outer, longer than wide. Those beyond heptagonal, with strongly 

 concave inner lateral and outer sides, the former corresponding to 

 the tentacle pores ; much longer than wide, widest at the outer 



Fig. 1, Ophiostiha hldekii. x20. a. From above, h. From below, 

 c. Side view of three arm joints near disk. 



