!9 21 ] Schmitt: The Marine Decapod Crustacea of California 291 



Current "it really is the part of the Japan Stream bordering the 

 Pacific Coast, and doubtless would not have been given a different 

 name were it not for its low temperature and relatively greater 

 velocity." (McEwen, 1915, p. 133.) 



It is these two great, as it were compensating influences, the one 

 warming a northern, normally cold region, and the other cooling a 

 southern, normally warm region, which tend to equalize the tempera- 

 tures along the greater part of the west coast and to make possible 

 the large faunal area which extends from about the eastern Aleutian 

 Islands to near Magdalena Bay, Lower California. 



These conditions are graphically portrayed, in a general way, in 

 Berghaus's Physical Atlas (1892, pis. 21 and 22, "Seestromungen"), 

 but our present detailed knowledge concerning them is almost entirely 

 due to the researches conducted by Dr. G. F. McEwen under the 

 auspices of the Scripps Institution (1910, 1912, 1915, 1916). 



A number of students of the west coast fauna, chiefly conchol- 

 ogists (Dall, 1899, 1909, 1916, and Bartsch, 1912, also Torrey and 

 Verrill above), attach great importance to Point Conception as a 

 faunal barrier. Possibly their conclusions are influenced by a pre- 

 dominance of littoral (sensu strictu), or shallow-water forms. These, 

 especially in the case of mollusks, always reflect extremely localized 

 environments, and were they excluded and only those of less restricted 

 (bathymetric) range considered, i.e., 25 to 50 to 100 fathoms, no 

 doubt Point Conception as an apparent faunal barrier would cease to 

 be significant. Of the California decapods, only twenty-eight (15%) 

 are at present restricted to the region north of Point Conception and 



winter. Also, it appears that the annual range of off-shore temperatures agrees 

 with the normal range for the same latitude. But the inshore temperatures are 

 notably less than the others for the same latitude, especially during the warmest 

 part of the year, and consequently have less than the annual normal range. Again, 

 the maximum and minimum temperatures occur in-shore some months after the 

 corresponding normal times; and the variation of in-shore temperatures with 

 respect to the latitude is scarcely half the normal amount." (McEwen, 1915. 

 p. 134.) 



Surface Temperatures at Latitude 30, 150 Miles South of San Diego 



Average ocean temper- Temperature of the Pa- Temperature of the in- 



atures for the whole eific at the boundary shore water along 



circle having the giv- of the California and the Pacific coast, 



en latitude. Japan currents. 



Time of Time of Time of 



Temp, occurrence Temp, occurrence Temp, occurrence 



Maximum 77° August 72° Aug., Sept. 65° September 



Minimum 64° February 61° April 59° May 



Annual range .... 13° 11° 6° 



Surface Temperatures at Latitude 40°, off Cape Mendocino 



Maximum 66° August 66° September 57° October 



Minimum 48° February 51° April 52° March 



Annual range .... 18° 15° 5° 



