10 CALIFORNIA ACADEMY OF HCIENCES. 



Dr. James Perrin Smith, Professor of Paleontology in Leland Stanford Junior 

 Universit}', has had general supervision of this paper during its preparation. He has 

 accompanied the writer on journeys that covered much of the territory under dis- 

 cussion, and has offered many valuable suggestions regarding the faunal relations 

 and stratigraphy of the San Pedro formations. 



The writer is indebted to Dr. John C. Branner, Professor of Geology in 

 Leland Stanford Junior University, for valuable suggestions in regard to the field 

 work and compilation of this paper. 



Dr. William Healey Dall, of the United States National Museum, has 

 identified numerous specimens sent to him, acknowledgment for which is given 

 with each species. Dr. Dall has also prepared the diagnoses of the family Pyrami- 

 dellidse, and has furnished drawings of the species of that family, and for the corals; 

 and in many otli.er ways has extended courtesies during the preparation of this work. 



Dr. John C. Merriam, of the University of California, has given free access to 

 all of the collections under his charge; has extended many other courtesies; and has 

 offered suggestions which have added to the value of the paper. 



The writer is indebted to his father, Delos Arnold, for the use of his collec- 

 tion; for notes and suggestions on the stratigraphy of the San Pedro deposits; for 

 assistance in the prej^aration of the drawings; and, most of all, for the interest mani- 

 fested by him in procuring the material upon which much of this paper is based. 

 The field work and collecting has been done as much by him as by the writer. For 

 the past fifteen years he has made numerous visits each year to the San Pedro beds, 

 and to his untiring efforts is due the discovery of such a large number of species 

 in them. He has also visited and made systematic collections from the deposits 

 of Santa Barbara, Ventura, San Diego and other localities along the southern 

 California coast. 



Acknowledgment is also due to Mr. T. Wayland Vaughan, Dr. R. E. C. 

 Stearns, Mr. Henry Hemphill, Dr. A. A. Wright, Mr. J. Howard Wilson, 

 and others. 



The illustrations are from drawings by Dr. J. C. McConnell, Misses Winnifred 

 M. Paine and Fanny H. Mitchell, Messrs. H. R. Johnson, R. E. Renaud and 

 R. Arnold. 



Where the types of new species belonged to Delos Arnold, these types have 

 been deposited in the United States National Museum at Washington, and, where 

 possible, duplicates will be dej^osited in the paleontological collections of the California 

 Academy of Sciences, and of Leland Stanford Junior University. 



