1913] The Ottawa Naturalist. 81 



interradius 1, but this when magnified about 20 diameters reveals 

 a striated surface as if belonging to a sea-urchin. 



Vertical Section. 



XI. The last item of evidence to be here given from the 

 oral skeleton is derived from the sequence and form of outline 

 of the vertical section given in text figure 1 . 



Fig. 1. Outlines from vertical section of P. narrawayi passingjin 

 through one interradius to center and out by one of the interradii next 

 the opposite radius. Slight offsets have been made to include suboral 

 epineurals and secondary jaws. 



It is not a difficult matter to account for these plates, their 

 form and position, if the outline is that of the true oral surface. 

 If, however, this outline is of the aboral surface of the oral 

 skeleton, we are face to face with an apparent lv insuperable 

 difficulty. How are we to explain the presence of the deep 

 concavity on the now aboral inner face of the marginal the 

 large paired plates which now become supra-orals the beveled 

 interior faces of the mouth plates and the function of the 

 "secondary jaws." Are we to suppose that the circumgastric 

 ring of ten radially situated pieces (our first epineurals) rested 

 against or over the borders of the stomach and served for 

 "internal massage" or for a compress to aid in the emptying of 

 the stomach cavity? Was the ring of ten doubledieaded internal 

 "crusher^ of the oesophagus" an essential adjunct of this new 

 and wonderful mechanism? Those against an oral aspect must 

 explain this apparently senseless arrangement of heretofore 

 whollv unknown plates. Should further study establish their 

 view we may properly expect that the biological story told by 

 these plates will be one of intense interest. 



The Aboral Skeleton. 



The balance of Dr. Raymond's evidence is contained in 

 the paragraph commencing on p. 106, line 44, of his criticism 

 and is derived from the plates marked (x) and (y) in our plate 

 VIII, fig. 1. I agree with him that for these "a place cannot be 

 found in the structure of the specimen " (p. 106, lines 45-46). He 



