1915.] NATURAL SCIENCES OF PHILADELPHIA. 45- 



During the present study, I have received great help from Dr. 

 Hubert Lyman Clark, of the Museum of Comparative Zoology, in. 

 the loan of many precisely determined specimens from that Museum 

 and in helpful advice; my best thanks are due to him. This paper 

 is in fact an outcome of his suggestions. A more detailed monograph 

 with illustrations will be published ultimately in Japan. 



The outbreak of the present war has made it impossible for me to- 

 receive some specimens of Palaeozoic ophiurans promised me by 

 Dr. B. Sttirtz, so that I am obliged to defer a revision and classifica- 

 tion of Palaeozoic ophiurans to the future. 



The greater part of the present study was done in the Zoological 

 Institute of the Imperial University of Tokyo, and the type speci- 

 mens of all the new species described belong to it. 



Sendai, Japan, December 1, 1914. 



Subclass I. CEGOPHIUROIDA nov. 



Ophiuroidea with external ambulacral grooves, and without 

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

 shields 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. Adambulacral plates, i.e., lateral 

 arm plates, subventral. Madreporite either dorsal or ventral, 

 often large and similar in shape to that of an Asteroid. 



This subclass consists chiefly of Palaeozoic genera. 



The CEgophiuroida lack all the fundamental characters by which 

 Recent ophiurans are clearly distinguished from Asteroids. Indeed, 

 the distinction of the present subclass from the cryptozonial Aster- 

 oids depends merely upon the different development of certain, 

 common structures. 



Subclass II. MYOPHIUROIDA nov. 



Ophiuroidea without external ambulacral grooves, and with 

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

 shields and dorsal arm plates usually present; but sometimes rudi- 

 mentary or absent. Ambulacral plates opposite, usually completely 

 soldered in pairs to form the vertebrae. Madreporite represented 

 by one, or sometimes all, of the oral shields. 



This subclass includes certain Palaeozoic forms and all the ophiurans 

 since the Mesozoic. 



