The subgenusBoleosoma is herein restricted to include:Etheostoma olmstedi, E. nigrum, E. perlongum, E. longimanum, andE. podostemone. Members of the subgenus lack nuptial tubercles, the males darken during the breeding season and females have bilobed genital papillae. The following three species are excluded from the subgenusBoleosoma: Etheostoma jessiae andE. stigmaeum, males having elongate genital papillae (considerably shortened in males ofBoleosoma) and brightened breeding coloration;Etheostoma chlorosomum, males having breeding tubercles and less than half the lateral line scales pored.
Etheostoma olmstedi possesses a complete infraorbital canal versus incomplete inE. nigrum; and usually 13 pectoral rays versus 11 or 12. Four subspecies ofE. olmstedi are recognized: (1)E. olmstedi olmstedi has poorly scaled nape, cheek, breast, and belly and is restricted to slow-moving, upstream habitats. (2)E. o. atromaculatum is strongly scaled, tolerant to low salinities and restricted to downstream base-gradient and river habitats. (3)E. o. vexillare is a Rappahannock River endemic with little head and belly squamation and fewer than 43 lateral line scales. (4)E. o. maculaticeps has two anal spines (other subspecies have only one) and weak head and belly squamation.
Within the Rappahannock RiverE. o. vexillare has been found as far downstream as the falls at Fredricksburg, where it occurs sympatrically withE. o. atromaculatum; there they act as species.E. o. olmstedi is found in minor pool-and-riffle streams tributary to the Rappahannock below the falls but in this river is not in contact withvexillare. However, a zone of intergradation exists in the upper Pamunkey River betweenvexillare andolmstedi. E. o. olmstedi andE. o. atromaculatum have been found together in tributary streams of the Chesapeake Bay in situations similar to those described by Trautman (1957:568) forE. nigrum nigrum andE. n. eulepis. E. olmstedi atromaculatum may have been widespread in tidal streams of the exposed continental shelf during periods of lawered sea level of the Pleistocene. But with rising post-Pleistocene sea levels, it has been forced into closer contact withE. olmstedi olmstedi in tributaries to the main rivers of the Bay below the Fall Line.
BothE. olmstedi olmstedi andE. o. atromaculatum returned to the Lake Ontario plain in New York following the final Wisconsin retreat There is evidence thatE. o. olmstedi moved over the divide from the upper Susquehanna into upper Fall Creek near Ithaca at earliest post-glacial times, although the Horseheads outlet probably accounted for its widest dispersion northward. Later, as pro-glacier lake levels fell, routes from the Hudson through the Mohawk valley were opened and this route westward was utilized byE. o. atromaculatum. When these two subspecies met in a broad reoccupation of the Ontario basin, isolating mechanisms broke down and intergrading populations there now demonstrate broad intermediacy in head squamation. Hudson River, stocks of these two subspecies may have existed in some refugium off the present coast of New Jersey during the period of greatest glacial advance and sea level decline. Although both subspecies now exist in the Delaware basin, it is less likely that they used stream capture to move northward from the Delaware River system into the Hudson valley.
South of the Rappahannock RiverE. o. olmstedi is restricted to Coastal Plain environments. The upper reaches of both the James and the Roanoke rivers may have had appropriate habitat prempted by twoBoleosoma endemics,E. longimanum of the James andE. podostemone of the Roanoke, or by representatives ofE. nigrum also found in the Tar and Neuse rivers further south.E. nigrum may have originated east of the Appalachians and escaped by stream capture into the New River system of the Ohio or vice versa. The displacement ofE. olmstedi from the southern Piedmont favors the second alternative. Whatever transpired,E. nigrum now has eastern representatives but is more generally spread in the Mississippi system where it shows relatively little variation.
E. olmstedi maculaticeps is found in the Piedmont south of those streams having uplandE. nigrum representatives. The population of this subspecies in the upper Cape Fear River demonstrates relatively high incidence of incomplete infraorbital canal; a characteristic ofE. nigrum. Lack of any known major stream exchanges between headwaters of the upper Cape Fear and the Neuse River makes character introgression unlikely and suggests character convergence.E. o. maculaticeps populations within the Santee River system show clinal difference in numbers of lateral line scales; those upstream, have fewer than those downstream. South of the Santee, this subspecies shows relatively little geographic variation.