IO THE AMERICAN NATURALIST. [Vol. XXXVII. 



upper labials normal, while only 41, or 79 per cent, have nor- 

 mal lower labials; of the 38 females, 31, or 81.5 per cent, have 

 normal upper labials, while only 22, or 58 per cent, have the 

 lower normal. Thus, of 90 snakes, 81, just 90 per cent, have 

 the normal number of upper labials, while only 63, or 70 per 

 cent, have the lower labials normal. There is no well-marked 

 difference between the right and left sides of the head, though 

 it may be noted in passing that of 10 aberrations in superior 

 labials, 7 were on the right-hand side, while of 32 aberrations 

 in inferior labials, only 14 were on the right-hand side. It 

 may further be noted that of the 10 aberrations in superior 

 labials, all were due to added plates, while of the 32 aberra- 

 tions in inferior labials, only 20 were due to added plates. 



Comparison of Sipedon and Erythrogaster. 



Having thus made clear some of the peculiarities which dis- 

 tinguish males from females and adults from young, in the 

 water snakes under consideration, we may now pass on to a 

 careful comparative study of the two so-called "subspecies." 

 We do not need to stop and consider points of internal anat- 

 omy or those external characters which are common to both 

 forms and serve to indicate their position in the genus Natrix. 

 We will therefore take up those points wherein erythrogaster 

 differs from sipedon, and see how marked and how constant 

 those differences are. 



1 . Size. — There can be no question that erythrogaster is a 

 larger snake than sipedon. As yet I have not seen a really 

 small specimen of erythrogaster, while the smallest specimen 

 of sipedon captured must have been born only a few days 

 previously. The table at the top of the opposite page will make 

 the difference in size clear. 



The average erythrogaster is therefore considerably more than 

 25 per cent larger than the average sipedon. The contrast 

 between the sexes is much more marked in sipedon, though 

 even in erythrogaster the females are very decidedly larger. 

 The absence of small specimens of erythrogaster is one of the 

 most puzzling facts met with, and one for which it is difficult 



