THE AMERICAN NATURALIST. [Vol. XXXVII. 



size. That it is not a matter of sex is shown by the fact that 

 the females of erythrogaster average 1 5 1 .4 gastrosteges apiece 

 and the males 150.8, while msipedon the females average 141. 7 

 and the males 142.9. These differences seem too small to 

 have any significance. That the number of gastrosteges is 

 not dependent on size is shown by the fact that the five largest 

 sipedonsy averaging 1066 mm. in length, have only 143.8 gas- 

 trosteges each, while the five smallest, averaging only 440 mm., 



have 144.2 gastrosteges each. Comparing erythrogaster and 

 sipcdon, without reference to age or sex, we find that the 

 former has on the average 151 gastrosteges, while the latter 

 has only 142. But the difference between the two forms is 

 made most apparent by the accompanying diagram (III). 



It will be seen at once that 148 is the maximum number for 

 sipcdon, and, at the same time, is the minimum number for ery- 

 throgaster. It ought to be stated that occasionally an imperfect 



