CAMBRIAN GEOLOGY AND PALEONTOLOGY 



V 



No. 2.— CAMBRIAN AND LOWER OZARKIAN TRILOBITES 



By CHARLES D. WALCOTT 



(With Plates 9 to 14) 



INTRODUCTION 



The field work of the past decade has resulted in the accumula- 

 tion of extensive collections of fossils from the Cambrian and Lower 

 Ozarkian formations. In order to aid in the delimitation of geologi- 

 cal formations preliminary studies were made of portions of the 

 material and names assigned to supposedly new genera and species. 

 A few of these have been used in published lists and the study of 

 the brachiopods published."^ Realizing that the publication of" generic 

 and specific names of the trilobites without description and illustra- 

 tion was of little service it was decided to print from time to time 

 the new genera and species. In this paper are presented in an outline 

 form characterizations of those genera which were ready for pre- 

 liminary publication. These are presented at this time to meet the 

 needs recently expressed by a number of field workers. No attempt 

 has been made to group the genera in biological or geological order. 



Dr. E. O. Ulrich has been studying the faunas of the Copper Cam- 

 brian and Ozarkian formations, especially of the Mississippi province 

 for many years, giving special attention to the trilobites. When un- 

 published genera and species were found in the collections that 

 he had already identified and named his work was accepted, which 

 explains the reference to unpublished species and genera by Ulrich. 



It was thought that outline drawings of the type species would 

 present in the most concise manner possible the characters of the 

 genera. These drawings are to be regarded as preliminary and 

 subject to correction as better material becomes available. 



AMECEPHALUS new genus 



PI. 9, fig. I. (Nat. size.) Diagrammatic outline of the type species as 



restricted. 



Amecephalns includes those forms with the wide frontal border 

 that were formerly referred to the type species. 



^ Smithsonian Misc. Coll., 67, No. 8, 1923, and 75, Nos. i and 9, 1924. 



Smithsonian Miscellaneous Collections, Vol. 75, No. 2. 



53 



