1921 J Schmitt: The Marine Decapod Crustacea of California 289 



San Diego, and these two were both common to the other two localities. 

 At San Diego, however, the- opportunities for collecting were compara- 

 tively limited, and but a short time was spent at that place. ' ' 



That neither Fraser, Torrey, nor Coe considered the region south 

 of San Diego, and that thirty-three of the California decapods at 

 present find the southern limit of their range at San Diego is no doubt 

 due to the extreme dearth of material from the west coast of Lower 

 California. Except for the explorations of the elder Anthony 

 (A. W.) and a number of scattered stations of the "Albatross" the 

 littoral portion of this region remains today almost as much a "terra 

 incognita" as it was before the expeditions of the California Academy 

 of Sciences to Magdalena Bay and the "Cape." It still offers an 

 extremely fertile field for the ambitious collector. 



But Dr. A. E. Ortmann (1896a) was the first to point out the 

 continuity of the faunal region under discussion, with whose "Pacific 

 Boreal (Littoral) Subregion, " lying south of the Aleutian Islands 

 it closely corresponds. 



Unlike almost all other students of zoogeography who seem to have 

 followed the inductive method and constructed their zoogeographical 

 divisions according to the actual distribution of animals, Dr. Ortmann 

 followed the deductive method and constructed his divisions according 

 to the differences in the physical conditions influencing the distri- 

 bution of animals. Of these "probably no single factor is a more 

 effective barrier to the extensive geographical range of marine animals 

 than is that of temperature" (Mayer, 1914, p. 3), for, to use the 

 words of Doflein (1904, p. 269), "Alle Erfahrungen der letzten Zeit 

 haben uns mehr und mehr gelehrt, dass die Verbreitung der Meeres- 

 tiere am meisten von den Wassertemperaturen beeinflusst wird. " 



Torrey, Coe, and Verrill all realized the importance of the in- 

 fluence of temperature on the distribution of the forms upon which 

 their studies were based. 



Though Dr. Torrey spoke of his faunal differences as being cor- 

 related with certain geographical differences, he said (1902, p. 7) : 



North of the [Alaska] peninsula is a region whose waters are largely covered 

 with ice for more than half of each year. South of the peninsula begins a vast 

 stretch of coast which is washed by the comparatively warm waters of the Japan 

 Current. This current is probably accountable for the absence of abrupt transi- 

 tions between the faunal area which I have tried to schematize above [quoted 

 on p. 287 of this paper], and the exceedingly long distances to which some of the 

 northern species have been distributed southward. The temperature of the current 

 varies gradually with latitude, however, and that offers some explanation for the 

 small faunal differences that exist. 



