PREFACE. 



The writer has, for the past eleven years, been collecting 

 Triassic fossils in California, Nevada, and Idaho, and study- 

 ing the Triassic stratigraphy. This paper is intended as a 

 summary of the work done, and only a few of the most 

 characteristic species are figured and described. There is 

 now in press by the United States Geological Survey, a 

 work by Alpheus Hyatt and James Perrin Smith on the 

 " Triassic Cephalopod Genera of America," in which every 

 cephalopod genus is described, and one representative 

 species under each one, known to occur in the Trias of 

 North America, is described and figured. The writer has 

 also in preparation, for the United States Geological Survey, 

 a monograph on the marine Triassic invertebrate fauna of 

 North America. 



In view of the early appearance of the former of these 

 publications only the most diagnostic species are figured in 

 the present paper. 



James Perrin Smith. 



Stanford University, California, 

 November 17, 1903. 



(i) [323] July 23, 1904. 



