342 AKT. 2. — H. MATSUMOTO : 



mastix mixta Lütken, 0. ammlosa (Lamaeck), 0. lütkeni Pfeffer 

 and Ophiarthrum elegans Petees. In all of them, the radial 

 shields are very stout and boot- shaped, and each consists of a 

 radial bar and a transverse vring projecting laterally from the 

 outer part of the former. Each shield has two articular condyles 

 and one pit, fitting to the two condyles and one pit of the 

 corresponding genital plate. The latter is bar-like, slightly curved 

 laterally, articulating with the genital scale at some distance 

 inwards from the outer end. The genital scales arc also b9,r-like, 

 more or less flattened, but not so wide and leaf -like as those of 

 the Gnathophiurida. The peristomial plates are rather small and 

 double, the two being firmly united together. The oral frames 

 are exceedingly stout, with extremely well developed lateral wings 

 for the attachment of very voluminous masticatory muscles. The 

 oral and dental plates taken together are "IT- shaped in dorsal view, 

 the former completely overlapping the latter. They are quite 

 different from those of the Gnathophiurida. The teeth are quad- 

 rangular and very stout. 



In Ophiopsila riisei Lütken, 1859, the internal structures are 

 almost similar to those of the preceding, save the radial shields, 

 which are slender and bar-hke, without transverse wings, and 

 rather closely set in pairs. Ophiopsila is by no means near to 

 the Amphiuridce in internal structures, so that I have no hesita- 

 tion to refer it to the present family, forming however a sub- 

 family for it alone. 



Key to Japanese genera of Ophiocomidœ, 



A — Disk covered with granules or bearing spines. 



a — Disk covered only with granules, entirely free of spines . . OpJdocoma. 



