THE AMERICAN NATURALIST. [Vol. XXXVII. 



It will be seen that the females of the two forms agree 

 remarkably in length of head and tail, while the male sipedons 

 show only a very slight and unimportant increase over the 

 males of the other form, and this slight increase is doubtless 

 due to their very considerably smaller size. The one important 

 point brought out by this table is that erythrogastcr has a much 

 larger eye than sipedon, the average difference being over 2 

 per cent. This is very noticeable in living and freshly killed 



snakes, but it is obvious in preserved specimens. Of the 27 

 specimens of erythrogaster, none had the eye less than 4.5 mm. 

 in diameter, while 20 had it 5 mm. or more, and in four of 

 these it was 6 mm. Of 63 specimens of sipedon, on the other 

 hand, only six had the eye more than 4 mm. in diameter, and 

 in only two of these did it measure 5 mm. The accompanying 

 diagram (II) shows at a glance the relative size of the eye in the 

 27 erythrogastcrs and the corresponding 27 sipedons (8 largest 

 females and 19 largest males). In this diagram, percentages 



