A Census of the Land and Fresh-water Mollusks of 

 Southwestern California. 



Harold Hannibal. 

 GENERAL REMARKS. 



The recent visit oi* Dall, the appearance of a new edition 

 of "'West Coast Shells," and the promise in time of a depend- 

 able manual of the "marines" has given an added stimulus to 

 interest in conchology in southern Calif ornia, a bit of the world 

 which, during recent years, has contributed generously toward 

 the increase and diffusion of knowledge along this line. This 

 has resulted in several requests for a systematic account of the 

 land and fresh-water shells of the region. 



Realizing that, with the frequent changes perpetrated m 

 the nomenclature, a mere check-list would shortly occupy a po- 

 sition of honor among the concholo^ieal antiquities, while these 

 same alterations and numerous others to follow before the 

 classification is placed on a strictly 'genetic basis, preclude the 

 preparation of a contribution as extensive as a manual, an 

 attempt has been made to embody the desirable features of 

 both in the following pages. The usefulness of a check-list is 

 thereby retained, but the paper possesses the added advantage 

 of value «to one who would delve into the intricacies of "why 

 and wherefore." 



The portion dealing with the terrestrial species, in the 

 preparation of which, Mr. Henry M. Edson of Palo Alto. Cali- 

 fornia, has assisted, follows. Part two, which treats of the 

 aquatic forms, will appear in a succeeding number. 



The Los Angeles System. 



The area under consideration has been termed the Los 

 Angeles System*. This lies south of the great divide formed 

 by the crest of the Santa Ynez, San Gabriel, and San Bernar- 

 dino Mountains and westerly from the San Jacinto, Cuyamaca, 

 and San Pedro Martir Ranges. The bulk of the system falls 

 in southwestern California, but a narrow arm extends south 

 along the west coast of Baja California to the vicinity of San 

 Sebastian Viseaino Bay. it includes not only the California- 

 Baja California mainland, but the islands off the coast, the 

 Channel. Santa Barbara, Coronado, San Martin, and Cerros 

 groups. 



As regards terrestrial and aquatic mollusca the area com- 

 prises a natural fauna! unit. The fauna is partially interme- 



Wesl Coast Shells. 1910, p. 300, 



