1913] Michael: ><agilla califoniica frfJiii Snii Dirgo Region 113 



Width of Posterior Fix 

 3.92 per cent for animals between 24 and 26 mm. 

 .3.94 per cent for animal's between 22 and 24 mm. 

 4.28 per cent for animals between 20 and 22 mm. 

 4.11 per cent for animals between IS and 20 mm. 

 4.2.5 per cent for animals between 16 and 18 mm. 

 .S.42 per cent for animals between 14 and 16 mm. 

 3. .50 per cent fur animals between 12 and 14 mm. 



In the case of the length of the po.sterior fin there is an 

 indication of a possible negative correlation, the proportion 

 diminishing at the rate of about 0.0-5 per cent for an increase 

 of 1 mm. in length of animal. However, as the average pro- 

 portion, irrespective of the length, lies between 24.2 and 25.8 

 per cent, it is safe to conclude that the fin increases in length at 

 approximately the same rate that the animal does. 



VARIATION AND CORRELATION IN NUMBER OP 

 TEETH AND SEIZING JAWS 



The number of anterior and posterior teeth and seizing jaws 

 is regarded by most investigators as of maximum significance in 

 defining species of Sagiita. While I have suggested elsewhere 

 (1911, p. 68), that "variations in number of both anterior and 

 posterior teeth in many species is not referable to specific differ- 

 ences, but probably to some di.stribution factor," it is neverthe- 

 leas true that certain facts concerning their manner and rate 

 of variation are of considerable specific importance, as will be 

 seen in the following remarks. 



Number op Anterior Teeth. — Variation in numlier of an- 

 terior teeth is •well revealed in the following histogram (text 

 fig. 1), which shows that out of 191 tooth-rows counted in indi- 

 viduals varying from 9.5 to 2t; mm. in length none had less tluin 

 3 nor more than 7 teeth, while about 6 per cent had 3, 17 per 

 cent 4. 32.5 per cent 5, 37 per cent 6, and 8 per cent 7. Now, 

 while these frequencies, together with the rate of increase till 

 the maximum is attained, the rate of decrease thereafter, the 

 position of the maximum, and other features of the histogram 

 are definitely characteristic of the population considered, their 



