Vol. XI] BERRY— FOSSIL CHITOXS ^\J 



Pleistocene 

 Lower San Pedro Series: 



The Pleistocene chiton faunas are sufficiently extensive to 

 enable finer conclusions to be drawn. Recorded from the 

 Lower San Pedro are 19 species and subspecies. All are forms 

 which we know are accustomed to live between tides or in com- 

 paratively shallow water. Compared with the recent fauna 

 these show the following interesting relationships : 



Relations of Lower San Pedro Chiton Fauna with 

 Living Fauna of Corresponding Latitude 



Number of Per cent. 



species of total 



Extinct or unknown living 1 5.3 



Now living commonly in same region 8 42.1 



Now living in same region but more or less rare. . 4 21.1 

 Now living on other parts of the coast, but not 



known to occur in same latitude as fossils 6 31.6 



Now living more commonly to north than south. . 6 31.6 



Now living more commonly to south than north. . 



Known to occur only on shores to north 6 31.6 



Known to occur only on shores to south 



It is evident from this that the Lower San Pedro chitons 

 abundantly support Arnold's conclusions 4 that as compared with 

 the present, relatively "boreal conditions still preponderated 

 during this period." They show just as conclusively, however, 

 that these conditions were "cold" only in a relative way, and by 

 no means actually boreal as this term is generally understood 

 by the zoo-geographer. To one familiar with the recent chitons 

 this whole Lower San Pedro association is strikingly remi- 

 niscent of that which now occurs on the shores of central Cali- 

 fornia, notably Monterey Bay and the coasts of Monterey and 

 San Luis Obispo counties just to the southward. Not only are 

 all the species, save one Callisto chiton, still to be found 

 living in that region, but those most abundant and character- 

 istic in the Lower San Pedro are similarly abundant and 

 characteristic in the Monterey County fauna today. Among 

 the fossils it is quite true that when an attempt is made to apply 

 the reverse of this dictum a few conspicuous absences are found, 

 but these are very conceivably due to the incompleteness of the 

 record and may well be filled in later. In any event, nowhere 

 else in the recent fauna can be found such a peculiar assemblage 

 of species in association as Tonicella lineata, Cyanoplax hart- 



* :03, p. 66. 



