400 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



the recent fauna of the same region ; secondly, that both indi- 

 vidually and in associations of species, these animals are re- 

 markably definite in their latitudinal distribution ; and thirdly, 

 that this definiteness of geographical area inhabited extends 

 even more sharply to station as well. The bathymetric range 

 of most chitons is curiously narrow. 



It is accordingly the writer's belief that far from being justly 

 negligible, it is possible that the chitons will prove among the 

 best criteria for determining the age and relationships of any 

 formation in which they can be found with appreciable fre- 

 quency. It is in this connection, as well as the inherent interest 

 of one of our most characteristic, yet strangely neglected, faunal 

 groups, that this paper is chiefly of consequence. 



Acknowledgments 



Among the many who have furnished material aid during 

 the prosecution of this work, and to all of whom I wish grate- 

 fully to acknowledge my due indebtedness, I am under chief 

 obligation to Mr. and Mrs. Emery P. Chace of the Lorquin 

 Natural History Club of Los Angeles. They have been both 

 assiduous and successful in the search for additional material 

 and new horizons in the field, have been unfailingly generous 

 and self-sacrificing in the disposition of their specimens, and 

 have managed to maintain an enthusiastic interest throughout 

 the course of the investigations. 



Scarcely less credit belongs to Dr. Frank C. Clark of Santa 

 Monica and Los Angeles, who has ransacked his wonderful 

 material from the Pleistocene of his vicinity that no possible 

 specimen might escape examination, and to Mr. and Mrs. Frank 

 Stephens of San Diego, whom I must thank for many valuable 

 specimens, as well as field data, which in some cases have cost 

 them considerable trouble to secure. 



To Dr. William E. Ritter and the Scripps Institution for 

 Biological Research, under whose auspices the work was be- 

 gun and in large part carried on, I am indebted for aid of a 

 nature which has very much expedited the progress of the 

 work. 



Dr. Bruce L. Clark of the University of California has been 

 instrumental in securing me material for study, including the 

 interesting series of specimens from Vancouver Island Oligo- 



