50 The Ottawa Naturalist. [June-Juh 



in interradius 1 (plate III, fig. 3) is strongly suggestive of such a 

 plate with a genital opening. We should consider also the 

 possibility of developing, from our "secondary joint", a true 

 Ophiuroid torus with its spines. These suggestions are made 

 here for the purpose of calling attention to the fact that we are 

 in need of a consistent terminology that can be applied to all 

 classes of Echinoderms and because of the evidence which this 

 specimen, as yet only partially "developed", has to present 

 concerning this matter. It is suggested that we may inaugurate 

 a better terminology by using 'epineural" for "ambulacral" 

 in the Crinoidea, and using a new term altogether for the term 

 ambulacra as now used in the Asteroidea. Could I have used 

 "ambulacra" in place of " adambulacra " in this paper I should 

 have been glad to do so but the plates for which I would have 

 used this term are not the ambulacra of Asteroidea. 



Locomotion. 



The relatively short arms, the small number of marginal 

 ossicles, their flat and close fitting contiguous faces, the absence 

 of re-entrant angles for muscle fields and the marked broadening 

 of the arm as it approaches the disc all speak of rigidity. The 

 arm could neither be used for feeding after the manner of Asterias 

 nor could its lateral bending alone have been its means of loco- 

 motion. 



On the other hand if progress was by means of tube feet with 

 suckers, those long projecting epineurals would make a very 

 effective drag. We may esily recognize the difficulty of moving 

 this veritable harrow over seaweeds or dead shells on a hard 

 bottom unless the epineurals could so shift their position as to 

 adapt themselves to motion in any direction. If they could 

 thus give passive aid there is no reason why they might not 

 give active aid. Tube feet with suckers would be useless on 

 soft bottoms, such as that on which our specimen died, while 

 its spade like epineurals might be used to shift its position over 

 its feeding ground. 



Astropecten affords us an important suggestion. "Owing 

 to the loss of suckers it is unable to climb over rocks and stones 

 like the ordinary species, but it runs over the surfaces of the 

 hard sand in which it lives by means of its pointed tube feet." 1 

 The long and heavy epineurals moved by powerful muscles 

 ought at least to be as effctive agents of locomotion as pointed 

 tube feet. 



That some arm movement was allowed is shown by arm I 

 in fig. 3 of plate I. The tip is not only turned toward one side 



1 McBride, "Cambridge Natural History" Vol. I, Pa?e 468. 



