NO. 5 CAMBRIAN TRILOBITES 407 



in width of border ; width of frontal Hmb, and distance of eye from 

 posterior margin. 



A comparison with Mesonacis vermontana shows many points of 

 resemblance between the Appalachian and Cordilleran species. The 

 two are illustrated side by side on plate 45. 



Formation and locality. — Lower Cambrian: (35n) Mount Whyte 

 formation ; eastern slope of Mount Odaray, below McArthur Pass, 

 west-southwest of Lake O'Hara, British Columbia, Canada. 



For other localities, see Smithsonian Misc. Coll., Vol. 53, 1910, 

 pp. 329, 330. 



Order Proparia Beecher 

 Family Eodisciixk Raymond 



Eodiscid^ Raymond, 1913. Ottawa Nat., Vol. 27, p. 102. 



The discovery of the eye and free cheeks of Pagetia bootes and 

 P. clytia, with the facial sutures, cutting the margin posterior to the 

 eye and in advance of the genal angles, places this section of the 

 Eodiscida? with the order Proparia and carries with it the closely 

 related forms such as Eodisciis punctatus, E. scanicus, etc., that are 

 not known to have had facial sutures and free cheeks. 



For the species of the Eodiscidae that have eyes and free cheeks and 

 which otherwise are closely related to Eodiscus punctatus Salter, I 

 propose the generic name Pagetia. This genus represents a stage of 

 evolution of the free cheek and facial sutures corresponding to that of 

 Burlingia,^ but the large pygidium and cephalon indicate that it is an 

 instance of reversion in the free cheeks and facial sutures to a primi- 

 tive type, while the other parts of the dorsal shield indicate an 

 advanced stage of development. If this conclusion is correct, these 

 forms of the Eodiscidae support the view of Professor Swinnerton ^ 

 that the Proparian type is a reversion to a primitive type and not an 

 evolution through the Opisthoparia to a more advanced type. 



Genus PAGETIA, new genus 



This genus is proposed for the forms of Eodiscidae in which the 

 eye, the free cheeks, and facial sutures are developed. 



Genotype. — Pagetia bootes Walcott. 



Stratigraphic range and geographic distribution. — The two known 

 species occur in the Middle Cambrian, one {P. bootes) in the Burgess 

 shale member of the Stephen formation, north of Field, British 



^ Smithsonian Misc. Coll., Vol. 53, 1908, p. 14. 

 ''Geol. Mag., Dec. 6. Vol. 2, 1915. p. 545. 



