IO2 GIDEON S. DODDS. 



shoshonc (33 lakes out of 43) and Daphnia pulcx (27 lakes). 

 One or both of these species were found in 39 of 43 lakes in this 

 zone. Diaptomus shoshonc is a large and brilliantly colored 

 species, was described by Forbes from the Yellowstone, and has 

 been reported only from that region and high portions of the 

 Rockies in Colorado. It ranges into lakes far within the Canadian 

 Zone, but has by far its greatest abundance in the lakes and 

 pools above timberline. Daphnia pulcx is a cosmopolitan and 

 euthermic form but is much more abundant in these high lakes 

 than in any other part of the mountains, in fact is nearly want- 

 ing from the Hudsonian and Canadian, where it is replaced by 

 Daphnia longispina just as Diaptomus shosJwne is replaced by 

 D. leptopus var. piscina:. The variety of Daphnia pulex found 

 in these lakes is unusually large, and though subject to consid- 

 erable local variation, comes close to the form described from 

 the Yellowstone as D. clatJiatra by Forbes, where, too, it is as- 

 sociated with D. shoshonc. One of the striking and outstanding 

 features about zonal distribution in this region is this definite and 

 constant association of a species of Daphnia with one of Diapto- 

 mus. The two combinations are striking and constant, one 

 belongs definitely to the Canadian, the other to the Arctic-Alpine, 

 and the reverse combination is seldom met. Neither member of 

 the Canadian pair has been collected from lakes in the Arctic- 

 Alpine, and though both members of the alpine pair do sometimes 

 invade the Canadian, they usually go together and are found in 

 lakes where the other pair is wanting. Diaptomus coloradensis 

 is frequently found in the Arctic-Alpine but is of secondary im- 

 portance just as in the Canadian. 



Another species of importance in this zone is the fairy shrimp, 

 Branchinecta coloradensis which is commonly found in the pools, 

 though never in the lakes, along with Daphnia pulex and Diapto- 

 mus shoshone. This species was described by Packard from an 

 elevation of 12,000 feet on Gray's Peak, has been repeatedly 

 found in these high pools, and has come to stand as a type of a 

 distinctly alpine species of narrow range (Shantz, '05). Only 

 once have I collected it below the Arctic-Alpine, this at 9-575 

 feet, well within the Canadian Zone, and there is was associated 

 with the same species of Daphnia and Diaptomus as in the higher 



