AN ANNOTATED LIST OF THE SHELLS OF SAN PEDRO BAY AND VICINITY. UY Mrs. M. Burton Williamson. WITH A DESCRIPTION OF TWO NEW SPECIES BY W. H. DALL. (With Plates xix-xxiii.) I have often thought if the fauna and flora of every inhabited county in the United States were studied and reported by careful, conscien-tious lovers of nature, the contributions to the natural history of our country would be of no small value, not only as a record of the riches of nature but, at a future time, as a history of the life that at a certain period was identified with a particular locality. For there is nothing-permanent in nature. Her activity begets change, and change daily makes history. With these thoughts in my mind 1 have undertaken to give a list of the marine shell fauna of Los Angeles County found, for the most part, within a period of two years. 1 am indebted to Mrs. L. 11. Trow-bridge and Miss I. M. Shepard for lists of shells found by them. Some of their shells have been identified, through me, by Dr. J. G. Cooper, but the greater part, especially the rarer forms, have been determined at the Smithsonian Institution, Washington, D. C. Miss S. P. Monks, teacher of drawing and zoology in the State normal school, in Los An-geles, has kindly allowed me to examine the shells found by her as well as those in the museum of the normal school. There are still some shells that have not been identified. The Nudibranchiata are not included in this list. Doris and Eolis have been found in San Pedro Bay and at Catalina Island, but not specifically determined. INTRODUCTORY. The coast of Los Angeles County is diversified by two large bays, Santa Monica and San Pedro, with their long sandy beaches sepa-rated by high, rocky cliffs. On the northwestern coast of the county the Sierra de Santa Monica range of mountains rises abruptly from the ocean. The extreme Avestern point in this range is known as Point Dume, noted for its diatomaceous earth. Running hack from this point the coast curves in until it readies the sandy beach of Santa Monica Bay. In this bay Tivela crassatelloides and Tapes staminea 179 Proceeding National Museum, Vol. XV — No. 898.