368 ART. 2. — H. MATSUMOTO : 



6. Oral plates and frames long and slender. 



7. Distinct creases probably present between the interbrachial 

 ventral surfaces and arm bases. 



8. Dorsal arm plates entirely absent, or present only in a 

 few basal joints ; the dorsal side of the arms therefore largely 

 unprotected. 



9. Lateral arm plates with prominent spine ridges, which 

 extend to the ventral side of the arm ; those of the two sides 

 not meeting above or below, except in the very distal arm joints. 



10. Ventral arm plates higher in position than the lower 

 borders of the latei-al arm plates, so that the arm is longitudinally 

 grooved ventrally. 



I believe that, the Palaeozoic Myophiuroida are the stock from 

 which the recent ophiurans have been directly derived, because they 

 show no trace of peculiar specialisation and are fairly intermediate 

 in their organisation as a whole between the Œgophiuroida and 

 recent ophiurans. If this view be right, then the most archetypal 

 group of recent ophiurans must be looked for among those forms 

 which have the strongest resemblances to the Palaeozoic Myophiii- 

 roida. 



Certain genera of the Ophiolepididce, which are frequently said 

 to be primitive, appear to me to be far from being archetypal, 

 though they may evidently be paodomorphic. These genera in the 

 mature stage are in every feature similar to very young stages of 

 other ophiurans, having the disk covered only with the primaries 

 and radial shields, and the arms covered chiefly by the lateral arm 

 plates. But, the existence of such forms in the early ages of the 

 history of the Ophkiroidea is entirely unproved. As to the biogen- 

 etic law, VON Baer's view appears to me to be more consonant 

 to facts than F. Müllee's. The term "primitive" may mean 



