FURTHER STUDIES ON OHIO CRAYFISHES. CASES OF SYMPATRY OF STREAM SPECIES IN SOUTHERN OHIO

The two major stream species of crayfishes in Ohio are Orconectes propinquus sanborni (Faxon, 1884), and Orconectes rusticus rusticus (Girard, 1852). Orconectes rusticus rusticus and its subspecies are widely distributed over the exposed lime-stones on the flanks of the Cincinnati Anticline and occupy streams in the western half of the state. On the other hand, 0. p. sanborni seems to have developed in the old Teays River in areas where sandstone and shale predominated. Its present range includes the unglaciated plateau in southern Ohio. Thus, the zone of overlap of these two species forms an irregular north-south band across Ohio. Turner (1926) related this transition zone to the terminal moraine of the Illinoian glacier. In some respects it also closely approximates the easternmost exposures of Niagaran and Devonian limestones. Previous work has not shown just where and how the ranges of these two stream species join or overlap. While working on bottom organisms in Rocky Fork, Highland County, in 1951, I observed that 0. p. sanborni was the dominant stream species. During previous fisheries survey work I had found 0. r. rusticus in most of the adjacen