COLEOPTERA OF THE LOWER RIO GRANDE. qq 



to the writer that no one familiar with the Coleopterous fauna 

 of the United States can pick out more than five or six 

 which can be called characteristic of the Lower Sonoran zone, 

 though it is true that quite a number range into it; a number, 

 perhaps fifteen or sixteen, are tolerably characteristic of the 

 Upper Sonoran, while possibly twelve or fourteen are more 

 particularly tropical. The great majority are species of very- 

 wide distribution in eastern and central North America, many 

 of them extending even to the Canadian boundarv. No doubt 

 can be entertained however, that a studv of the phvtophagous 

 families will yield a larger percentage of Sonoran and Tropi- 

 cal species, since we may naturally infer that the carnivorous 

 beetles, of which the present list is mainly composed, are less 

 affected by peculiarities in the flora than the phvtophaga. 

 More will be said on the subject in the concluding number of 

 this article; for the present it will be sufficient to state the con- 

 viction that there is even less ground for considering the 

 Brownsville beetle-fauna as Lower Sonoran, than for classing 

 it as Tropical. The little jungles noted bv Mr. Schwarz, are 

 to be considered it seems, almost truly tropical, while on the 

 other hand, there are large areas of a verv different nature 

 surrounding these little forests, with a totally different coleop- 

 terous contingent. Some of these areas are, from their ele- 

 vated situation and dry climate, almost typicallv arid Lower 

 Sonoran. while the low-lying damp spots, not tropical, will 

 show a high percentage of forms common in humid regions 

 occupied by what Dr. Merriam has called the Carolinian and 

 Austroriparian faunas. In other words. Brownsville and its 

 environs are not in one life-zone but in at least two and proba- 

 bly three — the limits of these •• zones" being locallv irregular, 

 and determined not by temperature-conditions but bv those of 

 soil and humidity which through their action on plant life also 

 influence the insects. The only way in which these conditions 

 could be approximatelv indicated on a map would be bv spot- 

 ting it with appropriate colors as in mapping boreal or arctic 

 faunae on isolated mountain peaks. 



In compiling the list the writer has been fortunate in having 



