136 UNIVERSITY OF COLORADO STUDIES 



one extreme of climate possible for the insect, as with us maturity 

 seems only to be reached quite at the end of the season. 



The genus Tricorythus, nevertheless, has a much more northern 

 range ; for Dr. Needham also pointed out that his Canis ( ?) allecta, 

 from Ithaca, N. Y., should be known as Tricorythus allectus. 



The nymph of Tricorythus is not certainly known. The Ccenis 

 maxima Joly, from France (near Toulouse) was referred by Vays- 

 si^re to Tricorythus, and is provisionally accepted as such by Eaton, 

 though with considerable hesitation. It is known only from the nymph, 

 which is figured in detail by Eaton, and it is significant that no adult 

 Tricorythus has ever been seen in France or nearer thereto than Egypt. 

 This nymph has all the essential characters of a Ccenis, diflfering 

 only in slight details from the known members of that genus. Dr. 

 Needham (Bull. 86, N. Y. State Museum, p. 48) has described the 

 nymph of T. allectus, not, however, going into very minute details. 

 He has very kindly sent us some of these nymphs, stating, however, 

 that they were not bred, and that he is now doubtful whether they 

 should not be referred to Ccenis hilaris, which was found at the same 

 place. We find these nymphs to agree, so far as can be seen, with 

 CcBfiis, and it is perhaps safe to dismiss them as not pertaining to Tri- 

 corythus. 



There now remains the nymph collected near Boulder, at the locahty 

 of T. explicatus. It certainly has no intimate relationship with Ccenis 

 maxima, or with Dr. Needham 's specimens. These have the large 

 maxillary palpi of Ccenis, while ours has the same palpi greatly reduced, 

 and altogether as in the Ephemerella series. The mandibles of our 

 nymph greatly resemble those of Ccenis maxima, but they are not 

 unhke those of other allied genera. The maxillae are about as in the 

 "nameless ally of Ephemerella,^^ figured by Eaton in his monograph, 

 Plate 38, Figs. 4, 5. The labrum presents nothing especially ren:\3,rk- 

 able; the claws have about ten Httle denticles on the inner side; the 

 gill lamellae are not fringed; and while there is a large elytroid lamella, 

 as in Ccenis maximus and in true Ccenis, it is not subquadrate, but 

 triangular. There are no rows of dorsal hooks on the abdomen, so 

 that in Needham 's table of nymphs of the Ephemerella type ours falls 



