THE LIFE OF DEVILS LAKE 109 



Ostracoda arc subject and because of the variable and inconstant 

 nature of their surroundings, it is almost impossible to work out 

 their exact distribution." 



So far as I am aware the only attempts which have been made 

 thus far to compare the zonal distribution of plaucton with that 

 of higher animals have been those of Dodds (1920, 1924) in his papers 

 on Entomostraca and life zones in Colorado, who found (1920, pp. 

 104, 5) that ''The zonation is definite, even though the present collec- 

 tions do not enable as to discriminate beween all of the colder zones. 

 It is equally difficult, on the basis of our present knowledge to 

 sharpl}^ differentiate these same zones in their continental extent 

 in Canada and northern United States . . . Though these 

 zones have been established and defined on the basis of organisms 

 other than Entomostraca, j^et the agreement is striking and real, 

 and extends even to common species inhabiting the same zones 

 in localities hundreds of miles apart and separated by many 

 degrees of latitude." 



Marsh also in his chapter on the copepods in Ward & Whipple 

 (1918) points out the influence of temperature in limiting the dis- 

 tribution of certain species, but not of others. 



If we attempt to determine the life zone of Devils Lake or the 

 origin of its fauna on the basis of its entomostracan population we 

 find that the majority of its species are wide spread or cosmopoli- 

 tan in their distribution. These include the three species of Cy- 

 clops (viridis, leuckarti and serrulatus) and the Cladocera, Bos- 

 mina longirostris, Moiua macrocopa, Daphnia longispina, psittacea, 

 pulex and magna, Diaphanosoma brachyurum, Ceriodaphnia pul- 

 chella, Alona rectangula, Chj'dorus sphaericus and Simoeephalus 

 vetulus and the ostracod Cypris pellucida. Diaptomus sicilis has 

 hitherto been considered a cold water type restricted to the Great 

 Lakes and adjoining waters. Recent studies, however, have ex- 

 tended its area westward to Devils Lake and northward into 

 central Saskatchewan (Huntsman, 1922). 



D. leptopus piscinae occurs thruout the northwestern United 

 States, Alberta and Manitoba. D. shoshone occurs in mountain lakes 

 of the western United States and southern Canada. "The occur- 

 rence in Devils Lake is interesting in that it is out of the moun- 

 tains and is the most easterly location that has been reported."* 

 Its presence here brings it into the transition zone. 



D. siciloides. Its occurrence in the Devils Lake complex is 

 the most northerly yet recorded bringing this species into the 

 transition zone from the south. 



♦Letter from Dr. C. Dwight Marsh to the writer. 



