ON May 13, 1883, I chanced to enter a meadow a few miles above Washington, on the Virginia side of the Potomac, at the head of a small stream emptying into the river. It was between two hills, at an elevation of 100 feet above the Potomac, and about a mile from the river. Here I saw many clayey mounds covering burrows scattered over the ground irregularly both upon the banks of the stream and in the adjacent meadow, even as far as ten yards from the bed of the brook. My curiosity was aroused, and I explored several of the holes, finding in each a good-sized crayfish, which Prof. Walter Faxon identified as Cambarus diogenes, Girard (C. obesus, Hagen), otherwise known as the burrowing crayfish. I afterwards visited the locality several times, collecting specimens of the mounds and crayfishes, which are now in the United States National Museum, and making observations.