44 ROYAL SOCIETY OF CANADA 



off; a deep furrow runs across the glabella on the anterior third of it ; 

 its larger posterior portion bcai"S a short spinose projection. 



" The two thoracic annuli are divided by furrows and constrictionB 

 into nodular |)artiti(}ns, representing i-achis and ribs, but of too small size 

 to be accurately represented by a description, or by figures. 



" The pygidiura differs from the head-shield by the conical shape of 

 its rachis, terminating near the posterior margin in a bluntly pointed 

 end ; the median line of this rachis rises near the anterior end into a rod- 

 like crest, terminating in a backward projecting spinose protuberance ; 

 the anterior part of the rachis exhibit also an indentation by lateral 

 furrows." 



Mr. Walcott has identihed this species with A. interstrictus, White,' 

 but a comparison of the description and figure of this species with A. 

 montis will show a marked difference, especially in the form of the 

 glabella and the size of the rachis of the pygidium. 



Among the Agnosti of the Prospect Mountain limestone described 

 by Mr. Walcott,' the one most like this species is Agnostus bidens, whose 

 " cephalic shield " (a pygidium) is like the tail shield of this species in 

 form ; it differs however in having a narrower rachis, and in having that 

 divided in two lobes by a pair of transverse furrows. 



The Mount Stephen Agnostus differs from A. Sidenbladhi, an Upper 

 Cambrian species of Svveden, in the larger and longer rachis to the tail- 

 shield. It differs from A. fallax in the absence of lateral spines to the 

 pygidium. This species as figured b}" Linnarsson had no tubercle on 

 the main lobe of the glabella, nor defined front lobe to the rachis of the 

 pygidium. Later authors introduce these features. 



PTYCHOPARIA, Hawle and Corda. 



Pychoparia cordiller/E, Koem., sp. (PI. I., fig. 7.) 



Conocephalites cordillerœ, Roein., Acad. Nat. Sci., Phil., Proc. 1887, pt, i., p. 17, 



pi. i., fig. 8. 

 Ptychoparia cordillerœ. Wale, Aui. Jour. Sci., vol. xxxvi., Sept., 1888. 



Among the trilobites of the fauna of Mount Stephen, this is the only 

 one whicli has a specially Lower Cambrian aspect. As will be seen by 

 the authorities above cited it has been referred to more than one genus, 

 and might with as much propriety be relegated to a third. 



Dr. Roeminger's figure does not well re]iresent this species, which is 

 proportionately longer than his figure, and has eye-lobes more distant from 

 the glabella. 



> U. S. Geol. Surv. Bull. 30. p. 149, pi. xvi., figs. C and fia. 



* U. S. Geol. Surv. " Palii'ontology of the Eureka District," p. 2fi, pi. ix., figs. 

 13 and 13a. 



