10 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 122 



ratio tends to be lower in the Puget Sound population, the adults of 

 which are smaller than those of the other two populations. 



Origin of Variation in Cyphocaris challengeri 



Movement of Subarctic Water is from west to east, via the Sub- 

 arctic or Aleutian Ciu*rent (Sverdrup, Johnson, and Fleming, 1942). 

 As this ciu"rent approaches the American coast, it divides into the 

 Alaska Current, which moves north into the Gulf of Alaska, and the 

 California Current, which flows south along the coast of California. 

 From the direction of the currents it is assumed that the coastal 

 population of C. challengeri has been derived from the oceanic popida- 

 tion. Any large contribution of individuals to the oceanic population 



OCEANIC 



PUGET SOUND 



REVILLAGIGEDO CHANNEL 



.80 .90 1.00 I.IO 1.20 



Figure 8. — Ratio of length of basal process to that of distal segments of pereopod 5 for three 

 populations of Cyphocaris challengeri (for each diagram the horizontal line represents 

 the sample range, the vertical line the sample mean, and the black rectangle the value of 

 2 standard errors on each side of the mean; the distance from a mean to the edge of a 

 white rectangle equals the value of 1 standard deviation). 



from the coastal population is precluded by the circidation in the 

 coastal inlets. The inlets are deep estuaries, with a surface layer of 

 low salinity water formed by river runoff overlying a deep layer of 

 denser high salinity water. The surface water flows seaward and 

 deep water enters the inlets from the ocean. (Waldichuk, 1957; 

 Herlinveaux and Tully, 1961; Pickard, 1961). The effects of tides 

 and other factors complicate the pictiue, but if it is assumed that 

 Cyphocaris avoids the low salinity surface layer, the circulation would 

 tend to hinder its seaward movement. Hence, any genetic changes 

 that might accumiUate in the coastal populations would not affect 

 the oceanic population. 



The origin of the coastal forms can be explained by the mechanism 

 proposed by Buzzati-Tra verso (1958) and used by McGowan(1963) 

 to explain the distribution of two forms of the pteropod Limacina 

 helicina in the subarctic North Pacific. 



