Vol. XI] BERRY— FOSSIL CHITONS 449 



The evidence here is not altogether clear cut, but is easily 

 indicative of higher oceanic temperatures than prevailed dur- 

 ing the preceding period. This is better brought out when the 

 fauna of a single horizon is taken by itself, the conflicting evi- 

 dence being largely due to the peculiarities found in the faunas 

 of such exposures as those at Point Loma. Taken as a whole, 

 however, agreement is good with Arnold's statement ( :03, p. 

 66) that "the fauna of the upper San Pedro series is southern 

 in character, and, as would be expected, approaches more nearly 

 the present living fauna of the San Pedro region." The chitons 

 do not, however, well support his further conclusion that de- 

 position during this period occurred in shallower water than 

 during Lower San Pedro times. The chitons of the Lower San 

 Pedro exposures on Point Fermin, as we have already seen, 

 are practically exclusively shore species, a few only of which 

 have been found extending to a few fathoms depth. Those of 

 Long Wharf Canyon, which is unqualifiedly an Upper San 

 Pedro horizon, even though mainly shore forms, include a few 

 species like Leptochiton clarki and Ischnochiton sanctcemonica 

 which have the aspect of off-shore types from at least moderate 

 depths. No doubt different horizons within each period will 

 show considerable modifications in this respect. As an associa- 

 tion the Upper San Pedro chitons are not easy to bring into 

 correlation with those of any restricted region of the coast at 

 the present time. By itself, the Long Wharf Canyon fauna 

 is rather strongly reminiscent of that of the west coast of 

 Lower California in the neighborhood of the 28th parallel. This 

 impression is probably due very largely, if not wholly, so far as 

 the chitons are concerned, to the presence as a strong element 

 in the fauna of the now characteristically Lower Californian 

 Ischnochiton acrior. At the same time we find at the "coal 

 mine" locality on Point Loma, this same southern species oc- 

 curring simultaneously with the strongly northern Crypto- 

 chiton stellcri, an association which for the present we can only 

 regard as anomalous. Dr. Clark has so far failed to find the 

 slightest trace of Cryptochiton in all his quarrying and sifting 

 at Santa Monica. 



