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ROYAL SOCIETY OF CANADA 



generic characlors it appears to the writer that the fauna at Mount 

 Stephen cannot be older than the Peltura Fauna. 



Anotliei- view of the fauna, namely, the comparative abundance of 

 individuals leads to a similar conclusion. 



lleferring to the table on a former page it will bo seen that over two 

 hundred individuals (or parts of individuals) have been under review in 

 this examination of the Mount Stephen Fauna. From this number we 

 need to eliminate Agnostus and Ptychoparia, as giving no leading in- 

 dications. Bathyuriscus may aKso be taken out, as its affinities are 

 obscure. There remain 140 examples for comparison. Of these thirteen 

 only (the individuals that represent Dorypyge, Corynexochus and Doli- 

 chomeiopus) point to the Upper Paradoxides beds, the others indicate the 

 Peltura or a higher fauna. It is evident that this tenth (the 13) repre- 

 sents the dying fragment of an earlier fauna, and that the Mount Ste- 

 phen fauna is essentially Upper Cambrian. 



Comparative growth of the pj^gidium at the expense of the thorax 

 in Cambrian trilobites as shown by typical faunas. 



In the preceding discussion wo have regarded the trilobites of Mount 

 Stephen from the point of their genetic relationship, it might be well also 

 to consider them in relation to the development of the trilobites as a group. 



