Il8 UNIVERSITY OF COLORADO STUDIES 



species, for in many cases it is apparent that a given species very 

 probably occurs in a given area judging from its known distribution. 

 In Table i it may be seen that ten species of Colorado Amphibians 

 are species of wide range, since they are found on both sides of the 

 mountains and in several or all of the adjoining states. One species 

 deserves particular attention, Bufo boreas. As may be seen from 

 Tables 2, 3 and 4, the other species of our fauna have come in from 

 the south. This toad, however, is not found south of Colorado and 

 in the state is found only in the mountains in the montane zone. It 

 ranges north into Oregon where it is abundant. It must be considered 

 as either our only species of northern origin or a species left here in the 

 montane zone as the climate has become warmer since the retreat of 

 the glaciers. It may be noted that the terrestrial molluscan fauna 

 of Colorado is on the whole more closely related to the northern than 

 to the southern fauna. 



The snakes and lizards (Tables 2 and 3) are evidently species 

 which have come into the state from the south. That this migration 

 is still going on to some extent is shown by the addition to our fauna 

 in this report of four snakes, one turtle, one toad, one frog and one 

 lizard from the south. Three groups of reptiles exclusive of the turtles 

 may be noted: the first of seven lizards and five snakes which are 

 found on both sides of the range; a second of twelve snakes and seven 

 lizards found only east of the range; and a third of four snakes and 

 three hzards found only on the west side of the range. The last two 

 restricted classes are of course in general species of the Great Basin 

 Plains and of the Mississippi Basin. 



We have no records of turtles from the west side of the range in 

 Colorado (Table 4). It is probable that Kinosternon flavescens, 

 reported from Utah, and other Great Basin species will be found in 

 western Colorado. The relatively small number of species of this 

 group in our fauna is due largely to the lack of permanent sluggish 

 streams. Most of our streams are either too high and rapid in the 

 spring or too low in the summer for turtles. 



Of the adjoining states New Mexico has a greater proportion of 

 our fauna than any other, 47 of our 56 species occurring in that state. 



