494 



Gross Anatomy of Campeloma. 



The number of young is variable, the large mature specimens 

 containing, as might be expected, the greater number of young 

 shells. Twenty specimens were carefully examined with a view to 

 this feature, with the following result : 



These twenty individuals, therefore, present an average of forty- 

 three young. 



Aside from the tentacular differences which exist between the 

 male and female, both tentacles of the latter being uniformly sub- 

 ulate, a further sexual difference appears in the greater size and 

 somewhat more globose character of the female shell. Coordinated 

 with this difference in dimensions is the more shouldered character of 

 the whorls in the female specimen, a difference connected with the 

 position and necessarily large size of the gestatory sac. The males 

 are more regularly conical, with rather less oblique aperture, and 

 are of considerably less globose appearance than are the females. 

 This difference was supposed to be of value in determining the sex 

 when only the shell was at hand. To test it as a sexual differen- 

 tial character, thirty-six of the largest males and an equal number 

 of the largest females were selected from a finding of more than a 

 gallon of C. subsolidum, taken on August 6, 1887, and were care- 

 fully measured. The results appear in the following : 

 TABLE OF DIMENSIONS. MALES. 



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