COPEPODA 



757 



10 (n) Right and left fifth feet of male nearly equal in length, terminal 

 hook of right foot symmetrical. 



Diaptomus oregonensis Lilljeborg 1889. 



The most widely distributed of all North Amer- 

 ican species, and the one most likely to be collected 

 in the northern part of the United States. It is 

 found from one side of the continent to the other. 

 The most noticeable characteristic is the equal 

 length of the fifth feet of the male. 



Length of female, 1.5 mm. 



Length of male, 1.4 mm. 



FIG. 1176. Diaptomus oregonensis. 

 X 193. B, fifth foot of female. 



A, fifth feet of male. 

 X 200. (Original.) 



11 (10) Left fifth foot of male shorter than right 12 



12 (15) Left fifth foot reaching beyond first segment of right exopodite. . 13 



13 (14) Terminal hook of right exopodite uniangular, right endopodite 



equal in length to first segment of exopodite. 



Diaptomus reighardi Marsh 1895. 



This has been found in only four localities, Intermediate 

 Lake and Crooked Lake in northern Michigan, a lake on Beaver 

 Island in Lake Michigan, and Sodus Bay, N. Y. 



Length of female, 1.14 mm. 



Length of male, 1.02 mm. 



FIG. 1177. Fifth feet of male Diaptomus reighardi. X 145. (Original.) 



14 (13) Terminal hook biangular, right endopodite large, longer than first 

 segment of exopodite. 



Diaptomus mississippiensis Marsh 1894. 



The most common form of the Southern States; it is abundant all 

 through the states bordering on the Gulf. 



Length of female, 1.2 mm. 

 Length of male, i.i mm. 



FIG. 1178. Fifth feet of male Diaptomus mississippiensis. X 145. 



