i6 



JACOB REIGHARD. 



breeding red-horse in streams not less than thirty or forty feet 

 in width. 



2. Sexual Differences. There are no known color characters 

 by which the sexes of the red-horse may be distinguished with 

 certainty at any season but there are structural differences. 

 According to Forbes and Richardson (1908) the lower fins are 

 "longest in the male." Table II. has been made in the same 

 way as Table I. (See p. 8.) The averages were obtained from 

 five males and two females, all breeding fish. It shows that 

 all the fins of the male are longer than those of a female of the 

 same length with the possible exception of the caudal. The 

 caudal appears to be 5 per cent, shorter in the male. But since 

 some of the caudals are imperfect a comparison was made of a 

 single perfect male of 205 mm. with a perfect female of 280 mm. 

 on the basis of equal length. This shows that the upper lobe 

 of the caudal is 12 per cent, longer in the male and the lower lobe 

 33 per cent, longer. The latter value is included in parentheses 

 in the table. The anal and pectoral are longer in the male by 

 about 15 per cent. The dorsals and pelvics are longer by about 

 10 per cent. The lower lobe of the caudal of the male is not 

 only longer than that of the female, but about 14 per cent, 

 longer than the upper lobe. In the female the two lobes are 

 of equal length. 



TABLE II. 



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



OF Moxostoma aureolum OF EQUAL LENGTH, THE DIFFERENCE IN 



AVERAGE LENGTH OF FINS AND THE PERCENTAGE DIFFERENCE. 



The breeding males are further distinguished by the possession 

 of conspicious pearl organs. (Figs. 5, 6.) On the end of the 

 snout and sides of the head as far as the caudal margin of the 

 preoperculum are numerous large sharp-pointed organs, more 



