8 



JACOB REIGHARD. 



The difference between the sexes in fin length are shown in 



Table I. 



TABLE I. 



SHOWING IN MILLIMETERS THE AVERAGE LENGTH OF FINS IN MALES AND FEMALES 



OF Catostomus commersonii OF EQUAL LENGTH, THE DIFFERENCE IN 



AVERAGE LENGTH OF FINS AND THE PERCENTAGE DIFFERENCE. 



By fin length is meant the greatest distance from base of fin 

 to its margin, approximately the length of the longest fin ray. 

 The table is based on nine fish of which six were males. The 

 males ranged in length from 260 to 405 mm. with an average 

 of 312 mm. All had w r ell developed pearls. The females aver- 

 aged 263 mm. in length (210, 215, 365). In order to compare 

 fish of equal length the female average length has been made 

 equal to that of the male and the average fin lengths of the 

 females as obtained from measurements have been corrected in 

 proportion. The figures in the lower horizontal line therefore 

 show in percentages the sex difference in length of fins in fish 

 of the same length. Since the caudals of two of the females 

 were broken there is added for the caudal a corrected percentage 

 (31.1) obtained by comparison of a single male of 340 mm. length 

 with a female of 365 mm. 



From the table it appears that in fish of equal length the anal 

 and caudal (lower lobe) of the male are about 31 per cent, longer 

 than those of the female; the pectoral about 18 per cent, longer; 

 the pelvic about n per cent, and the dorsal only 5 per cent. 

 In the female the caudal lobes are of about equal length whereas 

 in the male the lower lobe in two perfect specimens averaged 

 about 10 per cent, longer than the upper. The fins appear to 

 differ in robustness in about the same proportion as in length. 

 This is shown by the width at mid-length of the longest anal ray 

 in a male and female of equal length; in the male 4.5 mm. in the 



