78 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.54. 



this zone, as may be seen from Table 4, are, for the most part, 

 euthermic forms ranging up from the plains. 



Montane zone. — To this zone I have assigned 63 bodies of water, 

 nearly all below 11,000 feet (the great majority below 10,500 feet). 

 In spite of peculiarities of different types of lakes, the f aural char- 

 acters of this zone are well defined and quite distinct from those 

 of either of the others. In this zone I have collected 35 species, 11 

 of which are confined to the zone, though on the basis of general 

 distribution 3 of these may be expected in the plains. Three 

 other species, evidently belonging primarily to this zone, are found 

 in one or two lakes each, at Boulder, just at the edge of the plains, 

 but not in plains lakes more remote from the mountains. In addi- 

 tion to these species there are the usual euthermic forms, common 

 at aU altitudes, which make a large part of the fauna of aU zones. 

 On account of the absence of lakes in the foothill region of the moun- 

 tains (between 5,400 and 8,100 feet) there are certain points about 

 the fauna of this zone in doubt, especially the nature of the transi- 

 tion between montane and plains zones. In describihg the fauna of 

 this zone it wiU be well to treat first the 49 lakes of the morainal 

 type, more or less stagnant in their nature, and later those directly 

 on the stream courses (14 in number). 



In the morainal lakes there have been found 34 species (including 

 all but one of those found in the zone), and in this region I think of 

 the morainal lakes as being typical of the zone. The characteristic 

 species, Diaptomus leptopus, var. piscinae (27 of the 49 lakes), is 

 confined to the zone except for one record by Marsh of its occurrence 

 in the lake on the university campus at Boulder. The most abun- 

 dant species is DapJinia longispina (39 lakes), which, though it is a 

 widespread species in temperate lowlands throughout the world, in 

 our region seems to belong, primarily, to the montane zone, for it is 

 not found at all in the alpine lakes, and on the planes of the State 

 it has so far been found in only one lake near Boulder, close to the 

 mountains. Here, as in the alpine zone, the frequent association 

 of two species (a copepod and a cladoceran) is conspicuous, and 

 the two above mentioned form a pair which, in the montane zone, 

 replaces the pulex-shoshone group of the alpine zone. In 43 lakes 

 one or both are found and in 23 both. Though neither member of 

 this pair has been found in any alpine lake, the members of the 

 alpine pair have been found in this zone, DapTinia pulex (14), Diapto- 

 mus shoshone (5 times), but there is only one case where all four 

 species have been collected from the same lake. 



In spite of this and other cases of partial mixing of these two faunas 

 the fact is quite evident that the two arrangements (pulex-shoslione 

 and longispina-lejHopus) are very much more frequent than either 

 of the other possible combinations of these four species, and it is 



