MONÜGRAPH OF JAPANESE OPHroßOlDEA. 3^17 



plates filling up the outer open angle formed by the other two ; while 

 in Ophiacantlia, OpliioUmna, &c., the peristomial plates are simple, 

 or double with soldered halves, always lacking the unpaired secon- 

 dary plate. Further, the peristomial plates are relatively to their 

 width distinctly longer in the former type than in the latter. 



When I compared a young specimen of Ophiarachia incrassata 

 with a specimen of Ophiurochceta mixta, kindly presented by Dr. 

 H. L. Claek, and with Kœhler's photographs of 0. Uttoralis, I 

 was instantly struck by the similarity in their plan of structure. 

 The only differences of Ophiurochceta from Ophiarachna are the 

 presence of the scattered disk spines and the absence of the 

 accessory oral shields, besides the smaller size. The systematic 

 value of the accessory oral shields is, however, scarcely recognised 

 by Claek. And I have also observed the absence of accessory 

 slaields in some interradii of a certain specimen of Ophiarachna 

 incrassata. One may wâtli good reason regard the relation of 

 Ophiurochceta to Ophiarachna to be parallel to that of Ophiomastix 

 to Ophiocoma or of Ophiochœta to Pectinura.^^ 



1) Claek, 1915, has i^rovisionally referred my OpMurochccta to Verbihl's Opfdotreta. The 

 l.atler genus, which includes six species .iccording to Claek, is undoubtedly too heterogeneous to 

 be looked upon as n distinct genus ; and I can find practically no common characteristic for these 

 six species. I look upon Veeeill's Ophiotreta merely as a section of the genuine Ophiacantha. 

 As Claek's Ophiotreta is A'ery heterogeneous, it is almost useless to compare my Ophiurochceta 

 with the rest of Claek"s Ophiotreta. So that I wish here to compare my Ophiurocho'ta with the 

 type of OphiotrePi. They differ as follows. 



OpMurochada : — Disk covered with fine granules, besides scattered spines ; oral angles regularly 

 triangular, regularly closing the oral slits, distinctly granulated; oral shields situated far in- 

 wards, so that the distance from their inner end to the tip of the oral angles is very short ; 

 no cluster of dental ijapillfc, though a few infradental papiUœ may be present ; orsal arm 

 plates fairly wide, so that the arm spines do not approximate dorsally ; ventral arm i)lates dis- 

 tinctly in contact with one another ; arm spines not extremely long, opaque and not serrate (at 

 least in adult) ; two tentacle scales lo each pore, the abradial one overlapping the base of the 

 lowest arm spine. 



Ophiacantha [Ophiotreta) Uneolata : — Disk covered with coarse granxxles, besides scatteretl 

 spines ; oral angles distinctly narrowed at base by the second oral tentacle pores, so that the 

 oral slits are gaping ; no granulation on the oral angles ; oral shields situated far outwards from 



