Gross Anatomy of Gampeloma. 

 TABLE OP DIMENSIONS. FEMALES. 



495 



I. length in mm. II. = diameter in mm. 



A comparison of ratios shows the numerical values of differ- 

 ences, as follows: Length of male to its diameter, -ff-Jf-f ; length 

 of female to its diameter, f-|- ffy ; length of female to length of 

 male, f^ ff-g- ; diameter of female to diameter of male, -J-f $.. 

 The differences of lengths is 5.561 and of diameters 2.893. It 

 would appear, then, that this degree of difference may be of diag- 

 nostic value in the matter of sex. The diagram, Fig. 3, is designed 

 to present this sexual peculiarity in a graph- 

 ic form. The marginal numbers represent 

 millimetres. The ordinates represent the 

 lengths, and the abscissas, which have the 

 same scale, represent diameters. The cir- 

 cular conventional sign represents the male 

 and the triangular character the female spec- 

 imen. The average dimensions of each 

 group are represented by the open conven- 

 tional sign with its distinguishing sex mark 

 conjoined. It will be seen that while the 

 dots fall into two pretty well-defined groups, 



the range of greatest variation follows the ordinates, and tha* this 

 range is comparatively greater for the female than for the male form. 

 In other words, the males are more constant in lengths and vary less 

 in diameter, while, for the female form, differences in length are 

 measurably compensated by corresponding increase in diameter. 



In connection with this character it may not be altogether amiss 

 to call attention to certain so-called species which have been based 

 upon the males of C. subsolidum. They are Campeloma milesii Lea, 



