INTRODUCTION AND ACKNOWLEDGMENTS. 



The field work upon which this paper is based began in the winter of 1886, 

 when the writer first visited the fossil-bearing beds of San Pedro. Since that time 

 several visits have been made each year to the beds in that vicinity, generally after 

 heavy rains, when landslides and the breaking off of the banks have given new 

 exposures. The specimens obtained during these excursions are in the collection of 

 the writer's father, Delos Arnold of Pasadena, California, and have furnished most 

 of the material on which the present paper is based. It was first intended to 

 compile a list, with synonymy, of the fossils of San Pedro and vicinity, but the scope 

 of the paper has been enlarged until the present work is the result. 



One of the obstacles met with in the preparation of this work has been the 

 lack of systematic information in regard to the fauna and stratigraphy of the Pleisto- 

 cene of the Pacific Coast. Dall, Cooper, Gabb, Ashley and Merriam have published 

 notes on the faunal aspects of the marine Pleistocene of the coast of California; while 

 Whitney, Lawson, Fairbanks and Ashley have contributed to our knowledge of the 

 geology and stratigraphy of the Pleistocene. The inadequacy of these observations 

 has led the writer to visit as many localities as possible in the endeavor to obtain 

 information that would add to the knowledge of the Pliocene and Pleistocene of 

 California. Enough evidence was obtained at the different points along the coast to 

 warrant the statement that we have in the California deposits the greatest develop- 

 ment of the marine Pleistocene in the world. Future investigations are necessary 

 in order to give more accurately the thickness of the sediments deposited and 

 the amount of orogenic movement which has taken place since the beginning of 

 the Pleistocene epoch. The future study of the Pleistocene fauna will no doubt 

 add greatly to our knowledge of the relations existing between the Tertiary and 

 living faunas. 



Besides the collection of Delos Arnold, the writer has had access to the 

 collections or material belonging to the following institutions or individuals: 



1. Leland Stanford Junior University: Geological Department collections. 



2. University of California: Geological Department collections. State Geo- 

 logical Survey collections, and State Mining Bureau collections. 



3. California Academy of Sciences: Paleontological and Conchologieal 

 collections. 



4. The private collection of Mrs. M. Burton Williamson, Los Angeles, 



California. 



5. The private collection of Mrs. T. S. Oldroyd, Los Angeles, California. 



6. The private collection of Mr. Henry Hemphill, San Diego, California. 



. 2 , [ 9 ] September 22, 1902. 



