CAMBRIAN BIVALVED CRUSTACEA OF THE ORDER 

 CONCHOSTRACA 



By E. 0. Ulrich 



Of the United States Geological Survey 



and 



R. S. Bassler 



Of the United States National Museum 



INTRODUCTION 



The present work is the outgrowth of investigations of the Pale- 

 ozoic Ostracoda pursued by the authors as opportunity offered. In 

 the course of these studies a critical comparison with the Cambrian 

 species referred by authors to the Ostracoda became desirable. Most 

 of these Cambrian bivalved species have been described in the papers 

 published by Dr. G. F. Matthew on the Cambrian faunas of New 

 Brunswick and Nova Scotia. The types of Doctor Matthew's 

 species are now in the collections of the Royal Ontario Museum of 

 Paleontology at Toronto. Upon application to the Museum author- 

 ities some years ago, and through the courtesy of Prof. W. A. Parks, 

 the described specimens were very kindly sent to us at Washington 

 for restudy. 



When, at that time, Dr. Charles D. Walcott learned that the types 

 of Matthew's species of bivalved Crustacea were in our hands, he 

 suggested that we include in our studies the abundant material of a 

 similar nature contained in the unrivaled collection of Cambrian 

 fossils in the United States National Museum. This additional task 

 being accepted, the material in hand had become so nearly a complete 

 representation of the smaller bivalved Crustacea (Conchostraca) of 

 the American Cambrian that its treatment assumed the character 

 of a monograph rather than the brief notes on the supposed Ostracoda 

 described by Matthew. 



It should be said that we have been especially careful in the matter 

 of illustrations. With very few exceptions the new figures are all 

 photographs that have been touched up just enough to attain that 

 desirable medium stage between the authors' interpretation and the 



No. 2847.— Proceedings U. S. National Museum, Vol. 78, Art. 4. 

 2607—31 1 1 



