3o8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



comparing the Lower Cambrian fauna of the St. Lawrence-New- 

 foundland area with that of the Lower Cambrian Mount Whyte 

 formation of the Canadian Rocky Mountain region adjoining the 

 Canadian Pacific Railway. In these widely separated areas we find 

 Corynexochus senectus and the closely related forms of Bonnia — 

 C. (B.) parviiliis and C. (B.) fieldensis — associated' with typical 

 forms of the Mesonacidae, two of which are illustrated on plate 45 

 of this paper. I hope in a future paper to consider this subject both 

 from its stratigraphic and paleontologic aspects. 



The genus Corynexochus may have been the primitive type from 

 which the more highly developed genera Bathyuriscus and Dolicho- 

 metopiis descended, or it may be that they had a common ancestor in 

 early Lower Cambrian time. My first conclusion was to refer 

 Bathyuriscus to the Bathyuridse, but as the relations with Corynex- 

 ochus became more apparent it seemed more in accord with what 

 appeared to be the natural evolution of the Corynexochidse to con- 

 sider Bathyuriscus as linked with Corynexochus in a line of descent 

 that passed into Dolichometopus. This would place the Bathyuridse 

 as an offshoot from some Bathyuriscus-\ike ancestor in late Cambrian 

 or early post-Cambrian time. 



The Middle Cambrian genera Olenoides, Neolenus, and Orycto- 

 cephalus have in the glabella, palpebral (ocular) ridge and pygidium 

 characters that serve to bring the family Oryctocephalidse Beecher 

 close to the Corynexochidse, and it is possible that Olenoides and 

 Neolenus should be placed under the latter family or a subfamily of it. 



I now have a considerable series of undescribed Cambrian trilo- 

 bites that have been grouped under genera and species, and of which 

 figures have been made for illustration. These will be studied and 

 descriptions prepared for publication as opportunity permits. 



DESCRIPTIONS OF GENERA AND SPECIES 

 Family Corynexochid^ Angelin 



Corynexochidse Angelin [1852] 1854, [1878] Pal. Scandinavica, 2d. ed., 1854, 



p. 59. (Names family under genus Corynexochus but does not describe 



it.) 



Opisthoparia with cephalon and pygidium subequal in size or with 



pygidium smaller than the cephalon. Glabella usually expanded 



anteriorly and with only narrow limb and border in front. Eyes of 



medium to large size, with strong palpebral lobe and with palpebral 



■ See lists accompanying description of Corynexochus senectus (pp. .321-322). 



