20 



CANADIAN FOSSILS. 



and which appear to be the homologues of the ambulacral plates of 

 the rays in the genus Feniremites. The width of the rays near the 

 centre is two lines, and there are four of the small transverse or 

 ambulacral ossicula in the length of one line. The specimen does 

 not shew the centre of the ventral surface, so that we cannot deter- 

 mine whether the mouth was situated there or not. In order to 

 exhibit the analogy or affinity between this genus and Pentremites, I 

 have had the following figures prepared : — 



Figure 5. 



Fig. 5. 



Fig. 6. 



The ventral surface of Pentremites pyriformis (Say), d, the deltoid 

 plates, extending only half the length of the pseudambulacra. 



The ventral surface of Blastoidocrinus carcharicedens. d, the deltoid 

 plates, extending the whole length of the pseudambulacra. The 

 unshaded space in the centre is most probably the place of the 

 mouth. 



Fig. 7. 



Pig. 8. 



Figure T. Side view of P. pyriformis. 



" 8. The same, but with the deltoid plates extended to the extremities of 

 the pseudambulacra, as in B. carcharicedens. 



From the above figures it appears quite probable that the large 

 triangular plates of this species are the exact homologues of the 

 deltoid plates of the Pentremites. If we imagine a pentremite with 

 its deltoids so greatly developed that they would occupy the whole 



