•4KT. 18. ENTOMOSTRACA FROM COLORADO DODDS. 5 



of the other species from this lake have also a significance as belonging 

 to mountain lakes, but none of them are definitely related to the 

 alpine zone as distinct from other mountain elevations. Bald 

 Mountain Lake, 52 meters above timber line, doubtless also belongs 

 to the alpine zone, but its fauna, as represented in the collections, 

 is too scant to be of significance, except for the presence of Daphnia 

 pulex. 



Michigan Lake, 288 meters below timber line, while at nearly the 

 same elevation as Dead Lake, has a decidedly different fauna, one 

 which relates it to a lower zone in agreement with the 63 lakes of the 

 Tolland region assigned to the Montane (probably Canadian) zone. 

 In this lake are found as the dominant species Daphnia longispina 

 and Diaptomus leptopus, var. piscinae in place of the two species of 

 these genera found in Dead Lake. In two other lakes, Heart and 

 Fish, this is also the case, while in Ribbon Lake these two species 

 are also very abundant with a few individuals of Daphnia pulex in 

 one of the collections. It has been shown clearly in the Tolland 

 region that Diaptomus shoshone belongs to a higher group of lakes than 

 does D. leptopus, var, piscinae, and though no very definite alti- 

 tudinal difference is apparent in the Pike's Peak group, probably 

 because the number of lakes is few and they are at not greatly differ- 

 ing altitudes, it is quite probable that the same significance attaches 

 to these two species here as in the Tolland region. In making 

 studies of altitudinal zonation it is a striking fact that local condi- 

 tions often change the biotic conditions, so that zonal boundaries are 

 ragged. In the Tolland region, while the two species of Diaptomus 

 did unquestionably belong to two different altitudinal regions, there 

 were a few scattered lakes containing D. shoshone well within the area 

 occupied in the main by D. leptopus. It was also a striking fact 

 in the Tolland region that in mountain lakes where Diaptomus sho- 

 shone was present the species of Daphnia present was pulex, and that 

 when Diaptomus leptomus was present, Daphnia longispina rather 

 than pulex was present. In hardly any instance were both species of 

 Diaptomus found in the same lake nor both species of Daphnia. 

 The collections of Shantz show the same relations to exist in the 

 Pike's Peak lakes between these four species. They have been 

 selected as ''zone indicators" because when present in a lake they 

 are usually there in considerable numbers and because they appear 

 to give a consistent separation between zones. 



Other species of significance in the mountain group of lakes, as 

 belonging to mountain rather than to lowland lakes, though not of 

 use in dift'erentiating between the zones within the mountains, are 

 Macrothrix montana (described by Birge from Pike's Peak material 

 and so far not reported from other localities), Latona setifera, Pleuroxus 

 procurvatus, and Diaptomus nudus, which belong to the colder zones, 



