SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. 69 



Descriptions of Some Undescribed Fossil Shells of 



Pleistocene and Pliocene Formations of 



the Santa Monica Range. 



BY PROF. J. J. RIVERS. 



Dr. Ralph Arnold in his memoir of the fossils of San 

 Pedro published in June, 1903, made no mention of the species 

 now described. His very excellent treatise scarcely touched 

 upon the riches of the Santa Monica Range though he almost 

 exhausted the gifts of nature in fossil Mollusca of San Pedro 

 together with those yielded by the rocks of San Diego and 

 Santa Barbara. 



The Santa Monica Range has the same deposits as those 

 of San Diego, San Pedro and Santa Barbara judging from 

 the fauna found in this range. The San Diego Pliocene is 

 represented here by co-types of the following species : 



Ostrea veatchi Gabb., Pecten expansus DalL, Pecten hastatus 

 Sow., Pecten bellus Con , Pecten caurinus Gld , Pecteyi liemphilli 

 Dull., Pecten stearnsii Dull., Pecten op2intia Dall., Pecten svbven- 

 tricosus Dull., Pecten ventricosns Sow.. Pecten hericevs. Old., 

 Pecten subnodosns Dall and several other Pectens together with 

 Opalia varicostata Stearns and Pisania fortis Carp. 



The formations of Santa Barbara, San Pedro and San 

 Diego have each yielded Brachiopods, but the middle Pliocene 

 deposits of the Santa INIoniea Range have furnished all the 

 known species found hitherto discovered in the other three lo- 

 calities, viz : Terebratalia smithi Arnold. Terebratalia hem- 

 philli, Dall, Laqueus Jeffreys! Dall.. Laqueus calif ornicus Koch. 



Santa Monica Range furnishes a wide field of geological 

 investigation being rich in Pliocene deposits. There appears 

 to be three distinct Pliocene epochs; the oldest is a thick 

 deposit with few fossils and its matrix is formed out of the 

 first erosion of the Miocene and contains chunks of the shale 

 uneroded and fossils not yet identified. The strata has been 

 tilted to the perpendicular and crushed and crossbedded so 

 that when the fossils are disturbed they do not crumble but 

 break to pieces. 



The next older strata are the representatives of the San 

 Diego hard sandstone series yielding the Pectens. The later 

 Pliocene is the same as represented on Deadman's Island, San 

 Pedro. These are capped everywhere by Quaternary beach 

 gravels and by erosion debris as well as by glacial drift. The 

 canons of the coast yields glacial pebbles not profusely but 

 commonly and a student in geology can identify them' easily. 



Hyalaea tricnspida n. sp. 



Shell opaque white ; dorsal plate widely convex ; smooth on 



