NEW UPPER CAMBRIAN TRILOBITES 



By CHARLES E. RESSER 



Curator, Division of Invertebrate Paleontology and Paleobotany, 



U. S. National Museum 



(With 21 Plates) 



INTRODUCTION 



Soon after 1878 when Dr. C. D. Walcott centered his main efforts 

 on the study of the Cambrian system, he conceived the idea of a 

 monograph series, each of which should contain descriptions of all 

 Cambrian fossils representing a major animal group. With this in 

 mind he published new genera from time to time, frequently accom- 

 panied by descriptions of only one species, because the others were 

 left for the monograph. Thus, for example, brachiopod genera were 

 established and in 191 2 the monograph of this group appeared. Like- 

 wise trilobite genera were described with the view of producing such 

 a monograph in due course. For this reason practically all the genera 

 then known from the older beds were described in 1891.^ 



By 1920 it was clear that a monograph by him on Cambrian trilo- 

 bites, like that on the brachiopods, was not feasible. Nevertheless he 

 continued segregating specimens and in 1924 and 1925 published more 

 generic descriptions.^ In the two years remaining before his death in 

 1927 Dr. Walcott set aside some of the specimens here presented, and 

 less than 2 weeks before his passing he urged me to carry on and 

 describe species as rapidly as possible so that they would become 

 available for use. 



Since 1925 there has been increased activity in the study of Cam- 

 brian geology. Numerous papers describing many new genera have 



'Walcott, C. D.: 



1891. Fauna of the Lower Cambrian or Olenellus zone. loth Ann. Rep. 



U. S. Geol. Surv. 1891, pp. 507-774. 

 1916. Cambrian trilobites. Smithsonian Misc. Coll., vol. 64, No. 3, pp. 157- 



258, pis. 24-38. 

 1916. Cambrian trilobites. Ibid., vol. 64, No. 5, pp. 303-456, pis. 45-67. 

 ''Walcott, CD.: 



1924. Cambrian and Lower Ozarkian trilobites. Smithsonian Misc. Coll., 



vol. 75, No. 2, pp. 53-60, pis. 9-14. 



1925. Cambrian and Ozarkian trilobites. Ibid., vol. 75, No. 3, pp. 61-146, 



pis. 15-24. 



Smithsonian Miscellaneous Collections, Vol. 103, No. 5 



