CAMBKIAN BRACHIOPODA. 



By Charles D. Walcott. 



INTRODUCTION. 



PREPARATION AND SCOPE. 



It was not until after the preparation of the preliminary memoir, on the fauna of the Lower 

 Cambrian or Olenellus zone"' that I began to think seriously of undertaking the systematic 

 study of the Cambrian faunas of the world. The second extended contribution was the memoir 

 on tlie fossil Medusae/ after wliicli studies were continued on the Brachiopoda. Administra- 

 tive duties have greatly interfered -with the prosecution of the work, but by taking advantage 

 of all opportunities, both in the field and ofhce, some progress has been made from year to year. 

 The work is not so complete as it naight be in its discussion of genera and species, details of 

 evolution, and the relations of the Cambrian brachiopod fauna to Ordovician and later faunas. 

 My main purpose has been to make the results of the investigation of value to the student of 

 Cambrian faunas and to the stratigraphic geologist. 



This monograph includes the description of 44 genera, 15 subgenera, 477 species, and 59 

 varieties of Cambrian Brachiopoda, and of 3 genera, 1 subgenus, 42 species, and 1 variety of 

 Ordovician Brachiopoda. Of the Cambrian forms, 10 genera, 2 subgenera, 21 species, and 1 

 variety persist into the Ordovician. (See pp. 98-113 for complete tables giving distribution.) 



In this paper the Brachiopoda are treated in three ways — liistorically, geologically, 

 and zoologically. Historically the treatment comprises (1) a bibliography and (2) a table of 

 synonymic reference, giving a completely cross-referenced list of described species with the 

 present generic and specific reference of each. Geologically the distribution of the Brachi- 

 opoda is considered under the following headings: (1) General geographic and stratigrapliic 

 distribution; (2) detailed geographic distribution; (3) detailed stratigraphic distribution; (4) 

 habitat; and (5) fossil locaUties. Zoologically the discussion covers (1) the physical characters 

 of the Brachiopoda; (2) their distribution; (3) their evolution; and (4) their classification. 

 Lastly come the detailed descriptions of genera and species and the illustrative plates. 



ACKNOWLEDGMENTS . 



In the course of the investigations of the Cambrian brachiopods during the past ten years 

 I have received assistance in various forms and degrees from many individuals in all sections 

 of the world where the Cambrian strata and faunas occur. To all I return my most grateful 

 acknowledgment and sincere thanks. If any who have assisted me are overlooked in these 

 acknowledgments, I beg leave to assure them that it is not by intention. 



Dr. Ferdinand Schmidt, of the Royal Institution of St. Petersburg, sent many. specimens 

 and valuable notes on the range of the species in the Upper Cambrian and Lower Ordovician 

 Tjeds of the Baltic provinces of Russia. 



Dr. A. Mickwitz, of Reval, Esthonia, Russia, sent material from the Obolus beds of Russia. 



"Walcott, C. D., Fauna ot the Lower Cambrian or Olenellus zone: Tenth Ann. Rept. U. S. Geol. Survey, pt. 1 1890, pp. 609-763. 

 t> Walcott, C. D., Fossil Medusae: Mou. U. S. Geol. Survey, vol. 30, 1898. 



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