SEXUAL DIMORPHISM 167 



III. — Results. 



(a.) Conclusions. 

 In more condensed form the results given in the tables may be 

 expressed as follows. 



1. Males of Pleurohema, Elliptio, Symphynota, and Propter o 

 possess a greater height and degree oj inflation than females and are 

 relatively shorter. The females of Fusconaja, Amblema, Eiirynia, 

 L. luteola, and L. ovata show opposite characters in this respect to those 

 of females representing the first four named species. Also in the fore- 

 going, height correlates with the degree oj inflation of the shell. Males 

 oj Anodonta, Anodontoides while having a greater degree of inflation 

 than females, have a less height. 



2. Males of Elliptio, Anodonta, Paraptera, Anodontoides, Eurynia 

 and L. ovata have a relatively greater length of the posterior part of the 

 shell, and consequently less of the anterior. In the remaining shells 

 this condition is reversed. 



J. The one outstanding morphological feature associated to prepon- 

 derating extent with maleness in the Najades dealt with, ivas the 

 greater length of posterior liinge line, {the anterior seems best developed 

 in the females) . These facts correlate with values for anterior and 

 posterior length in yi the species only. 



4. Thickness of shell, as associated with sex, seems to be as equally 

 indifferent as all the other dimensions, {with the exception of those of 

 the hinge lines). 



{b.) Remarks. 



There is now given from Simpson, (6), Walker, (8), Utterback, 

 (7), all descriptive material of the external morphology of these 

 shells usually held to be associated with the different sexes. As a 

 rule, emphasis is placed on Walker's late work, and it is the writer's 

 desire to show the relation of this material to the results he has 

 obtained. 



Utterback believed females of Fusconaja and Symphynota to 

 possess a greater degree of inflation of the shell. My results check 

 only with the former in this respect. We must pass over the other 

 species listed in the order given (for the reason that there seems 

 to be no accredited descriptive material concerning their Sexual 

 Dimorphism), until we come to Paraptera. 



Simpson: Paraptera. "Female and male much alike, for-mer 

 sometimes a little rhomboid or again it ends in a wide rounded point 



