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University of California Publications in Geology [Vol. 9 



tions made by Mr. Studley. The two published lists supplemented 

 by Studley 's list are taken as the basis of comparison with the fauna 

 from the Santa Ana Mountains. 



A comparison of these faunas reveals the following species in 

 common between Chico Creek and the Santa Ana Mountains : 



Acila truneata (Gabb) Spisula chieoensis Packard 



Anomia lineata Gabb Spisula gabbiana (Anderson) 



Clisocolus dubius (Gabb) Tellina ashburnerii Gabb 



Crassatellites conradiana, var. tus- Tellina hoffmanniana Gabb (?) 



Spisula ashburnerii (Gabb) 



The number of species in common between the Santa Ana Mount- 

 ains and Chico Creek represent but about thirty-one per cent of 

 the number of determined species of the southern fauna, being nearly 

 the same per cent of the Chico Creek fauna. This small per cent of 

 identical species from the two localities is due in part to the fact 

 that the southern fauna, composed of three faunal zones, is compared 

 with the fauna from Chico Creek, represented probably by a single 

 zone. Seventeen out of the eighteen described species from the Tel- 

 lina ooides zone of the Santa Ana Mountains appear in the above list 

 of common species. On the other hand, there are but twelve out of 

 twenty-eight described species from the Aetaeonella oviformis zone 

 of the southern fauna occurring at Chico Creek. 



The much larger number of species in common between these 

 localities than was noted above in the comparison with the Horsetown 

 fauna indicates that the southern fauna is equivalent to at least a part 

 of the Chico from Chico Creek. 



The faunal differences may be more apparent than real, for the 

 fauna from Chico Creek is but imperfectly known and will be un- 

 doubtedly increased by subsequent workers. Nevertheless the differ- 

 ences demand consideration. 



It appears to be the consensus of opinion that differences of tem- 

 peratures due to the geographic positions of these two localities were 

 not as great during the Cretaceous as at present. This factor would 



cana (Gabb) 

 Cucullaea truneata (Gabb) 

 Dosinia inflata (Gabb) 

 Glycymeris veatchii (Gabb) 

 Inoceramus whitneyi Gabb 

 Meekia sella Gabb 

 Meretrix lens Gabb 

 Meretrix nitida Gabb 



Tellina ooides Gabb 

 Trigonia evansana Meek 

 Alaria faleiformis (Gabb) 

 Cinulia obliqua (Gabb) 

 Gyrodes expansa Gabb 

 Perissolax brevirostris Gabb 

 Volutoderma ealifornica Dall 

 Baeulites chieoensis Trask 



