178 



PROCEEDINGS OF THE ACADEMY OF 



[May, 



probable error of the single ratio and index was calculated. These 

 were based on twenty measurements of the three characters from a 

 single'shell. 5 The result of this was a probable error of ±.04 for 



Fig. 2. 



the index and ±.01 for the ratio. The probable error of the index 

 was greater as this character was more difficult to measure. H. B. 



See Mellor (1905), pp. 515-520. 



