The Productivity of Fish Food in Oneida Lake 249 



A NEW MAYFLY, C^NIS, FROM ONEIDA LAKE, 

 NEW YORK 



By Professor James G. Needham 

 Cornell University, Ithaca, N. Y. 



In the course of Mr. Frank C. Baker's collecting of aquatic 

 insects from Oneida Lake, N. Y., several specimens of nymphs 

 of a curious little mayfly, hitherto unknown to science, were 

 discovered. This little nymph I mistook for a member of the 

 similar in form and genus Ephemerella, it being, of the size 

 of a number of species in that genus, and more than twice 

 as large as any American species of the genus Ccenis hitherto 

 made known. Upon more careful examination, I find that 

 it is Ccenis and with conspicuous ocellar tubercles doubtless 

 allied to the Ccenis harrisella of Europe, the nymphs of 

 which are figured by Eaton in the Transactions of the Lin- 

 nean Society of London, second series, volume 3, plate 42. 



I have encountered this American species but once before. 

 A single specimen was collected by Professor T. L. Hankin- 

 son from the bed of Walnut Lake in Michigan on the 26th of 

 May, 1907. In the report of the Geological Survey of Michi- 

 gan, 1907, page 263, I made mere mention of it under the 

 name " Ephemerella sp." as follows : " A single curious larva 

 with prominent head tubercles was taken." This seems to 

 be in America an inhabitant only of lakes, though its Euro- 

 pean counterpart above mentioned is not. The species is 

 readily recognized by its remarkable head tubercles. It may 

 be briefly characterized as follows : 



Caenis lacustris sp. nov. 



Length 5-6 mm., antennae i^^ mm., caudal filaments 3 mm. 

 additional. An elongate species of generally pale coloration, 

 beautifully marked with brown. Head cuboidal with promi- 

 nent eyes capping the anterolateral angles. Three conspicu- 

 ous pyramidal horns arise from the three ocelli, each horn 

 surmounting a conspicuous black pigment spot. Body slender, 

 yet having three regions of enlargement, the prominent horned 



