MON0GR.y:'H OF JAPANESE OPHIUROIDEA. 367 



Phylogeny of the Ophiuroidea. 



It is very evident, that the forms with vertically coiled arms 

 are not archetypal, because th(^y have very solid and always 

 undivided vortebrœ, as mentioned in the introduction, while the 

 ophiuran vertebrae are palœontologically, as well as ontogenetically, 

 proved to be primarily divided. Thus, the OpMohyrsince, Trichas- 

 tericlœ, GorgonocephaUdœ, Ophiacanthidœ pars, Hemieuryalidœ, 

 Ophiaclince pars, and Ophiotrichidœ pars are eliminated from 

 primitive ophiurans. The forms with well developed lateral wings 

 of the oral fixâmes are evidently highly specialised. Thus, the 

 Amphiuridce, Ophiotrichidœ, Ophlolepidlnœ pars, Ophionereidince 

 and Ophiocomidce are eliminated from primitive ophiurans. The 

 remaining forms are the Ophiomyxlnce, Ophiocanthidce pars, 

 Amphilepididce, Ophiolepididœ pars, Ophioleucidce, OphiodermaUdce 

 and Ophiochitomnœ. Indeed, I have been able to find more or 

 less divided vertebrae in certain representatives of the Amphilepididce, 

 Ophioleindldœ and Ophiodermatidce, as well as of the Ophiomyxince 

 and Ophiacanthidœ. 



Though it is my purpose to discuss the results of a study of 

 Palaeozoic ophiurans in a future paper, I will here enumerate some 

 of the more important structures of Palaeozoic Myophluroida, as 

 bearing on the question before us. 



1. Disk covered with delicate scales or by a naked skin, 

 without distinct primaries. 



2. Kadial shields absent. 



3. Genital plates and scales absent. 



4. Oral shields absent. 



5. Adorai shields not very distinctly speciaUsed û'om the 

 lateral arm plates. 



