MONOGRArH OF JAPANESE OPHIUROIDEA. 5 



and " Ophioclueta " pars, i.e. my Ophkirochceta, may be clearly 

 distinguished from Ophiolimna emend, by certain internal struc- 

 tures. 



Prefixing so much, I now proceed to the exposition of my 

 own views, leaving them to be judged by their own merits. 



I have several representatives of Palœozoic ophiurans in hand, 

 and I purpose to publish a revision and classification of them in 

 the near future. 



The greater part of the present study was done in the 

 Zoological Institute of the Imperial University of Tokyo, to which 

 the type specimens of all the new species described in this paper 

 belong. Such new genera as Astrothanmus, Ophiosemnotes, Ilaplo- 

 pJiiura, Amphiopliiura, Ophiosonella, Ophiuroconis, OjjJiiurochceta, &g,, 

 are directly or indirectly based upon the specimens in Dr. H. L. 

 Clark's charge. All the text and plate figures in this paper were 

 drawn by me. 



Subclass I. ŒGOPHIUROIDA Matsumoto. 



Ophiuroidea with external ambulacral grooves and without 

 ventral arm plates. Radial shields, genital plates and scales, oral 

 shields, peristomial plates and dorsal arm plates also absent. 

 Ambulacral plates alternate or opposite ; in the latter case, they 

 may often be soldered in pairs to form the vertebrae. Adambula- 

 cral plates, i.e. lateral arm plates, subventral in position. Madre- 

 porite either dorsal or ventral, often large and similar in shape to 

 that of an asteroid. 



This subclass mostly consists of Palaeozoic forms, and lacks 

 all the fundamental characters by which the recent ophiurans are 

 clearly distinguished from the asteroids. Indeed, the distinction of 



