OF WASHINGTON. 341 



cially of the sharp demarcations in faunas and floras in Arizona 

 on account of the extremely variable altitudes, including isolated 

 peaks of considerable height and very low-lying desert regions. 

 The complexity of the life zones is thus more marked than else 

 where in the United States. He described at some length the 

 characteristic features, both botanical and entomological, of the 

 region mentioned, showing, among other things, that Dr. Mer- 

 riam's conclusion that the valley of the Colorado river is tropical 

 is not substantiated by a study of the insects. 



Inasmuch as many of the insects upon which Mr. Schwarz 

 had based his conclusions were captured at light, Mr. Howard 

 asked whether the species so collected were the best which could 

 be chosen to determine faunal limitations. Mr. Schwarz replied 

 that in that region a very great variety of insects is attracted to 

 light, beetles of almost every family being attracted in this way. 

 Mr. Ulke stated that in the East it is the beetles of the Lamelli- 

 corn series which are most numerously attracted to light, and Mr. 

 Schwarz said that in Arizona even Cicindelidae and water-beetles 

 (even where there is no water for many miles) are thus attracted. 



Mr. Howard referred to the fact that the tropical region of the 

 Colorado valley is extended by Dr. Merriam, in his recent maps, 

 far down the coast of Mexico along the eastern side of the Gulf 

 of California, but stated that from the determinations so far made 

 of a small collection of insects which he took at Guaymas during 

 the dry season in April of the present year, there was absolutely 

 no indication of a tropical fauna. Dr. Gill spoke of the land 

 shells of the Colorado river valley, and said that they afforded no 

 indication of a tropical fauna. Mr. Pollard said that with the 

 exception of a few characteristic plants the flora of the valley is 

 not tropical ; that is to say, it is not in the least comparable to the 

 tropical regions of the Florida Keys and the southern tip of Texas 

 about Brownsville. Mr. Schwarz, however, stated the fact 

 that there is a distinct difference between an arid tropical flora 

 and a humid tropical flora, instancing the flora of the extreme tip 

 of Lower California as a good example of arid tropical. Prof. 

 Uhler spoke of the genus Pachylis as an example of an arid trop 

 ical insect, feeding upon Opuntia, and distributed throughout 

 South and Central America, coming as far north as Fort Grant, 

 Arizona. He instanced several tropical genera among the He- 



