204 P. E. Raymond — Ceratopyge Fauna 



Aet. XVII. — -The Ceratopyge Fauna in Western North 

 America; by Peecy E. Raymond. 



The determination of the boundary between the Cam- 

 brian and Ordovician systems in the West has proven as 

 difficult a problem as it is in the East. The following 

 contribution to the discussion of this question is based 

 primarily upon a collection made by Mr. Francis P. Shep- 

 ard, a graduate of Harvard, in the course of the investiga- 

 tion of the structure of the Rocky Mountain Trench. 



The determinable fossils in his collections, from four 

 localities, in the Columbia River Valley, B. C, are : 



Lingulella moosensis Walcott, Hystricurus tubercidatus (Wal- 



L. ? allani Walcott, cott), 



Obolus mollisonensis Walcott, Cyphaspis ? brevimarginata 



Eoorthis desmopleura (Meek), Walcott, 



Eoorthis sp. ind., Symphysurus cleorus (Walcott), 



Dalmanellahamburgensis (Wal- 8. elongatus (Walcott), 



cott), Hcmigyraspis mcconnelli Ray- 



Syntrophia nundina Walcott, mond, 



Baphistoma nasoni Walcott, II. caribouensis (Walcott), 



Arthrorachis sp. hid., Megalaspis shepardi sp. nov. 1 



Menocephalus sp. ind. 



This is a good Ceratopyge fauna, comparable to that 

 which is found at the base of the Ordovician at many local- 

 ities in Europe. It lacks both Euloma and Niobe, but as 

 is well known, there is great variation in the composition 

 of this fauna in the different regions in which it is found. 

 Broegger long ago 2 called attention to its presence in the 

 Eureka District, in the lower part of the Pogonip. More 

 recently Walcott 3 has noted the same zone in British Col- 

 umbia, but listed only a very few species. The importance 

 of this fauna in the determination of the boundary 

 between the Cambrian and Ordovician is so great as to 

 justify a review of its distribution in western North 

 America. 



1 Not to burden this paper with detailed descriptions of fossils, Megalaspis 

 shepardi may be characterized briefly as follows : Known from pygidia only. 

 That shield elongate, sub-triangular, pointed behind. Axial lobe not prom- 

 inent, contracted near the middle, with about six faintly defined rings. 

 Pleural lobes nearly smooth, with one pair of obscure ribs. Shell strongly 

 punctate. Holotype collected by Mrs. Francis P. Shepard and now in the 

 Museum of Comparative Zoology. 



2 Nyt. Mag. for Naturvidensk/vol. 35, p. 229, 1896. 



3 Smithson. Miscl. Colls., vol. 57, No. 7, p. 229, 1912. 



