374 



ART. 2. — H. MATSUMOTO : 



the two subfamilies is by no means very great. So that, it may 

 not be very unreasonable to look upon the TricJiasteridce and 

 Gorgonocephalidce as having a blood relation att he very begin- 

 ning. 



Within the limit of the simple-armed, genera of the Gorgono- 

 cephalidce, the Gorgonocephcdinœ are evidently more archetypal 

 than the Astrotomhue, because the former have less specialised 

 and less localised oral and dental papillae and less powerful oral 

 angles than the latter, and the latter have well developed supple- 

 mentary plates in the spaces between the oral angles and the 

 interbrachial ventral surfaces. 



Another point to be noted is that the dividing of the arms 

 occurred independently in three groups, viz. the TricJiasterinœ, 

 Gorgono2ephalince and Astrotominœ, an example of parallelism due 

 to certain biological conditions. 



The interrelationships between the members of the Ophio- 

 myxinœ-\m.Q, or Phrynophiurida, may be shown as follows. 



Gorgonocephalin œ 



•with dividerl a,rms 



Astrotominœ 



with divided arms 

 I 



Astrotominae 



with simple arms 

 \ 



Gorgonocepliali ase 



with simple arms 



Tricliasteringe 



with divided arms 



Asterosclieraatinse 



Trichas teriuae 

 with simple arms 



Asteronychinre 

 Opbiobyrsinœ 

 Opliiomyxiuse 



