vol. 50 



Smithsonian 

 Miscellaneous Collections 



Vol IV Quarterly issue Part 4 



NEW AND CHARACTERISTIC SPECIES OF FOSSIL MOL- 

 LUSKS FROM THE OIL-BEARING TERTIARY FORMA- 

 TIONS OF SANTA BARBARA COUNTY, CALIFORNIA 



By RALPH ARNOLD 

 Paleontologist, U. S. Geological Survey 



Introduction 



During- an examination of the Santa Maria and Summerland oil 

 districts, Santa Barbara County, California, by the writer, assisted by 

 Robert Anderson and H. R. Johnson, in the summer of 1906, fossils 

 were found representative of several geological horizons in the Ter- 

 tiary. Many of these are well known or previously described species, 

 but some of them are new forms. In the following paper several of 

 the new forms are described and figured ; while a few of those pre- 

 viously described are simply figured, and a brief note concerning their 

 occurrence is inserted in the explanation accompanying each draw- 

 ing. It has been deemed advisable to insert figures of the old species 

 in this paper because the descriptions and illustrations of these forms 

 are in publications inaccessible to most readers, and it is essential for 

 the proper identification of the faunas that certain of the old species 

 be known. The differentiation of the various geologic formations 

 in the southern coast ranges of California depends almost entirely 

 upon their paleontology, so that it has been the aim of the writer to 

 give in this paper some of those species which will aid in the deter- 

 mination of the horizon of the various faunas found in that region. 

 These fossils, together with some others, will be figured on plates ix 

 to xvii, Bulletin 321, and plates xn to xxvi, Bulletin 322, U. S. Geo- 

 logical Survey. 



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