1912] The Ottawa Naturalist. 49 



III, fig. 1). The proximal ends of each pair of these plates were 

 cut to form a half circle and they could be drawn either aborad 

 to the ridge, or some distance orad. We here have another ring 

 of sliding joints aiding in food capture. The distal ends of these 

 epineurals seem to have retained a primitive central angle that 

 enabled them the better to hold their prey or to break the shells 

 of small mollusca. molluscoidea or Crustacea. These plates 

 could be raised or lowered and each pair could open and close 

 like a pair of pliers. The shifting of the position of their prox- 

 imal ends allowed them to assist in the capture of eggs, young, 

 or adult organisms up to 4 mm. m diameter and enabled them 

 also to press food into the space where the secondary jaws could 

 act upon it. 



The epineurals marked (2) were directed orad and their 

 attachments were along a diagonal edge which also rested in a 

 somewhat elevated socket on the oral edges of the interradial 

 marginals. The oral faces of these marginals also show the 

 fields of origin of the abductors of these more specialized first 

 and second epineurals. 



The remaining epineurals could function somewhat after 

 the manner of a duck's bill, for they could grub in the ooze and 

 press the mud out between the plates. When the epineurals 

 were all closed the captured and separated food contents could 

 be moved orad by a progressive wave movement (trough and 

 crest) of the ambulacral floor. The ability to shift the free ends 

 of the epineurals orad or aborad and to move either half of an 

 ambulacral floor would assist in the process. The evidence for 

 this manner of food getting is abundant and should be conclusive. 



The Homology of The Peristomial Plates. 



We must note that to carry the alternate arrangement 

 between epineurals and adambulacrals to the interradial mouth 

 angles and complete the paired series of epineural adductors 

 would require the presence of either a single unpaired epineural 

 or adambulacral in each interradius. If the primitive circlet 

 of peristomial covering pieces were five in number the "torus?" 

 may represent this primitive unpaired epineural. Figs. 3 and 5 

 of plate III (interradius 2) suggest such a derivation. If on 

 the other hand the odd plate was an adambulacral our "torus?" 

 might represent that plate. In the figures, however, it seems 

 too far removed from the adambulacrals to belong to the series. 

 What we have called the oral might be an odd adambulacral 

 and in this case we should consider the interradial marginal to 

 be the true oral. If the oral surface (left uppermost after death) 

 sank into contact with the ossicles of an aboral circlet then our 

 "torus?' ' might be an aborad interradial and the plate uncovered 



