NORTH AMERICAN DIPTERA. 45 



0% A !i»PEClE»< OF $i»I9IULrIUIVI FROM THF GRAIVD 

 CAIVOIV OF THE COLORADO. 



BY C. H. TYLER TOWNSEND. 



During the past Summer, larvae of a species of Simullmn were met 

 with very abundantly in a small streaiii in one of the branches of the 

 Grand Canon, July 8th to 11th. This branch, or side canon, is the 

 one down which the Hance trail leads, being situated about fifty-five 

 miles in a straight line N. N. W. of Flagstaff, Ariz. Ii is a deep 

 canon, about seven miles in length, and becomes boxed up in the 

 lower part of its course. About two miles down' in this canon a 

 small stream takes its source from a spring at a point about 2500 

 feet below the rim. After flowing for a few rods the stream sinks, 

 but reappears some distance down the canon, flowing on until it 

 reaches the Colorado River, into which it empties. In this stream 

 many colonies of the Slmuliuvi larvse were found in places where 

 the current ran swiftly over the smooth water-WH)rn surface of the 

 rock. In going up the stream from where it empties into the Col- 

 orado River to where it seeps out, a distance of fully three miles, 

 I counted fifty-two colonies of the larvte. There were six colonies 

 below the lower fall, where the stream drops about forty feet over a 

 shelf of rock (Archaean granite). It should be stated that the 

 point where this stream seeps out is about 3000 feet below the rim 

 of the canon, while the point where it empties into the Colorado 

 River is about 5000 feet below the rim. There is, therefore, a fall 

 of about 2000 feet in its uninterrupted course, or approximately 700 

 feet to the mile. The greatest fall is in the last mile or so. No larv?e 

 were found in the few rods of its upper course, between the spring 

 and the point where it sinks, the fall not being enough to form a 

 swift current. The depths given are those below the south rim, 

 which is 1000 feet lower than the opposite rim. The Colorado River 

 is, at this point, about 2500 feet above sea-level, and the south rim 

 about 7500 feet. These altitudes are from figures kindly furnished 

 by the United States Geological Survey. 



The larvse were of all sizes at this date, from very small to ap- 

 parentl}' h\\\y grown. In all cases they were attached to the smooth 

 eroded surfjice of the rock in the swifter current, but were once found 

 attached to leaves of grass growing in the stream. Empty whitened 

 or yellowed pupa skins and cases were discovered in patches in some 

 places. No live puppe were noticed at the time, but on subsequent 

 examination of material collected it was found that quite a percent- 



TR\NS. AM. ENT. SOC. XX. APRIL, 1893. 



