Among the fossil insects collected at Florissant, Colo, by Judge J. Henderson and Dr.F. Ramaley, of the University of Colorado, is a species of Corixidæ, represented by numerous individuals. It occurred, as Judge Henderson informs me, in the first railroad cutting east of Florissant, a little above the middle of the seciton there exposed. The shale containing the speciments is very much lighter than that in which the other Florissant fossil insects seen by me are imbedded, and it is believed to belong near the top of the series.