24 GARTH 



Lagoon- Viscaino Bay region, which show at least four additional Gulf 

 of California species occurring in this sheltered situation, but not else- 

 where on the open west coast. Species pairs found on outer and inner 

 peninsular coasts are Libinia setosa-L. mexicana, Herbstia parvifrons- 

 H. camptacantha, Randallia ornata-R. angelica, and Speocarcinus granu- 

 limanus-S. ferrugineus. The latter two differ from each other but slightly ; 

 their taxonomic status as full species is therefore in doubt. 



If the intertidal regions of the Gulf of California from Agua Verde 

 Bay on the west coast to Puerto San Carlos on the east can be added 

 to the warm-temperate Lower California west coast from Pta. Entrada 

 northward, we have in effect a Pacific Mediterranean region, of which 

 the present communication with the ocean, unlike the Strait of Gibraltar, 

 now lies within the tropics. That the present situation did not obtain 

 in the very recent past is indicated by the geological history of the 

 region. According to Beal (1948, p. 119), a rise of sea level of about 

 1600 feet occurred during the Pleistocene, reducing the peninsula to 

 about two thirds its present length and isolating the Cape district 

 south of La Paz. Communication was then possible across Magdalena 

 plain, opposite the southern limit of our warm-temperate region. The 

 difference between the two crab faunas is no greater than might be 

 expected from Pleistocene isolation. It is certainly less than that between 

 the Bay of Panama and the Caribbean, where the last confluence has 

 been dated as late mid-Pliocene. (Note: Beal's estimate should be revised 

 downward in the light of present knowledge concerning Pleistocene 

 fluctuations in sea level. A rise of several hundred feet is sufficient for 

 the purpose of this discussion, however.) 



All available evidence points to the conclusion that surface water 

 temperatures have been warmer in this area in the recent past, rather than 

 colder. A fossil find by Kanakoff (1948) in Newport Bay places Calli- 

 nectes bellicosus and TJca monilifera in the Southern California upper 

 Pleistocene fauna. The former now comes no farther north than Scam- 

 mon Lagoon, the latter is restricted to the Gulf of California. No later 

 than the middle of the last century warm water conditions prevailed 

 off central California, as shown by the Pacific Railroad Survey in con- 

 nection with fishes (Hubbs, 1948, p. 464). In 1859 Pleuroncodes planlpes, 

 a galatheid shrimp, occurred abundantly in Monterey Bay (Schmitt, 

 1921, p. 163) ; it now rarely comes north to San Diego and Santa Cata- 

 lina Island. 



The following figures are given by Ekman (1953, p. 143) for sur- 

 face temperatures in the northeastern Pacific as compared with the 

 northeastern Atlantic: 



