26 GARTH 



but discontinuous, and that their last strongholds are the rocky promon- 

 tories and headlands, the very sites at which upwelling occurs. 



In conclusion, it has been shown that there is a warm-temperate 

 marine fauna on the west coast of North America extending from Pt. 

 Conception to Pta. Entrada and including the northern part of the 

 Gulf of California. This has been done by considering the distribution 

 of the brachyuran Crustacea as a representative group with respect to 



(a) the number of endemic species and species-pairs occurring in this 

 region, and (b) the number of analogous species occurring in the cor- 

 responding Southern Hemisphere region of northern Chile and Peru. 

 That the warm-temperate region has not always been as closely delimited 

 as at present has been demonstrated by (a) the inter-glacial and post- 

 glacial history of the Lower California-Gulf of California region and 



(b) cyclical temperature fluctuations taking place ofF central California 

 during the past century. Reasons for the reduced size of the warm- 

 temperate region as compared to that of other continental shores, and for 

 the persistence in it of long-range boreal species are (a) the direction 

 and character of prevailing ocean currents and (b) the upwelling of 

 cold water near shore. The narrowness of the continental shelf is also 

 a factor in restricting the area that can be occupied by warm-temperate 

 benthic forms. 



