TRICORYTHUS, A GENUS OF MAYFLIES. 



By T. D. A. CocKERELL AND Marie Gill 



The genus Tricorythus was proposed by Eaton in 1868, to contain 

 a mayfly from Egypt, described by Pictet in 1 843-1 845 as a Ccenis. 

 Subsequently a species described by Burmeister in 1839 as Oxycypha 

 discolor, from the Cape of Good Hope, was added. Burmeister 's 

 genus Oxycypha consisted of two species of Ccenis and one of 

 Tricorythus; as Ccsnis Stephens dates from 1835, by the "ehmina- 

 tion method," followed by many zoologists, we should be obliged to 

 use the name Oxycypha for Tricorythus. The first species of 

 Oxycypha, however, was Ccsnis dimidiata. A third Tricorythus was 

 reported by Eaton in 1884 as coming from the Malay Archipelago, 

 but the species was not named, the material being inadequate for a 

 satisfactory description. 



So far, no species of the genus had occurred in America; but in the 

 Biologia Centrali- Americana (1892) Eaton described a new species, 

 T. explicatus, collected by Morrison in "Northern Sonora," which, 

 it is understood, may mean northwestern Mexico or southern Ari- 

 zona. The same species was recorded from Jalapa, Mexico, by Banks 

 in 1901, and from Copper Basin, Ariz., also by Banks, in 1903. On 

 October 7, 1905, many mayflies were found emerging from a stream 

 a few miles from Boulder, Colo. At the same time and place nymphs 

 were collected, but no flies were bred from observed nymphs. When 

 we came to examine the insects, we beUeved that we had a new species 

 of Canis; but Dr. Needham, to whom we sent specimens, kindly 

 pointed out that they were apparently Eaton's Tricorythus expli- 

 catus, and later enabled us to examine Eaton's description and figures, 

 which had not been accessible. Upon comparing our material with 

 the published account of T. explicatus, it was evident that the species 

 was the same, and that the range must be extended some hundreds 

 of miles northward. It is probable that Boulder represents nearly 



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