436 Simon Henry Gage 



The table for the sea lamprey shows clearly not only aver- 

 age greater length but also in each case the greater length 

 of individuals as compared with the lake lamprey. If one 

 compares the sexes it will be seen that the average female is 

 longer than the average male, thus reversing the conditions 

 obtaining with the lake lamprey. The proportions of the 

 body in the male and the female are more nearly alike than 

 in lake lampreys, but the variations are in the same direction 

 as with the male and female of the lake lamprey. 



THE BROOK LAMPREY. 



Petromyzon branchialis Linnaeus, (1758) Atnmocoetes brajichialh. 

 Cuvier, (1827). Plate IV. 



Until the spring of 1886 the brook lamprey was not known 

 in North America outside the Mississippi Valley (Jordan '85). 

 The reason for its non-discovery here before, is due to the fact 

 that so far as is known to the writer, it has never been taken 

 on the fish of the lake, and so far has only been found during 

 the .spawning season and immediately after transforming in the 

 autumn. Although the spawning grounds of the brook and 

 the lake lamprey are the same, the time of spawning of the 

 brook lamprey is earlier than that of the lake lamprey the two 

 forms never appearing together. This added to the facts that 

 at the earlier time the water is liable to be high and often tur- 

 bid, and that the size is small, the numbers comparatively few 

 and the coloration inconspicuous, it will be readily seen why 

 it might escape observation almost any where. 



In the spring of i885, while trying to determine the earliest 

 appearance of the lake lampreys on the spawning ground, 

 three male brook lampreys were found by Prof. S. E. Meek 

 and the writer. They were compared with specimens from 

 the Mississippi Valley and found to agree, and in our prelim- 

 inary paper at the American Association for the Advancement 

 of Science ('86), one of the points made was " The discovery 

 of Ammocoetes branchialis, [the brook lamprey] east of the 

 Mississippi Valley." 



By comparing the mouths of the lampreys in plate VI, the 

 Qharacter of the dentition will be seen to differ greatly from 



