Eighteen stratigraphic sections in the Valley and Ridge area of Virginia (10), West Virginia (6), Maryland (1), and southern Pennsylvania (1) were sampled in detail to establish the distribution of hystrichospheres in the Onesquethaw Stage of that region. The localities were chosen carefully relative to the stratigraphic and paleogeographic interpretation of Dennison (1961). Rock-stratigraphic units sampled include the Tioga Metabentonite, Huntersville Chert (including Bobs Ridge Sandstone Member), Onondaga Limestone, and Needmore Shale (with three subfacies: calcitic shale and limestone, calcitic shale, and Beaver Dam black shale).

No hystrichospheres were observed in the Bobs Ridge or other glauconitic sandstone beds in the Huntersville Chert. Only one fragmentary form was seen in the Tioga Metabentonite. The Onondaga Limestone, the three subfacies of Needmore Shale, and the chert of the Huntersville all contain hystrichospheres. Hystrichospheres are rare in Huntersville Chert adjacent to the Monroe Island of middle Onesquethaw age but are abundant in chert elsewhere. Similarly, they appear to be absent in all three subfacies of Needmore Shale adjacent to Monroe Island (at Covington, Virginia). Farther from land, in a basin toward the east between the island and a source of clastic mud near Baltimore, hystrichospheres are abundant in the calcitic shale and common in black-shale, calcitic-shale, and limestone su facies.

Nineteen species have been identified, assignable to Hystrichosphaeridium, Veryhachium, Polyedryxium, Michrystridium, and Cymatiosphaera. Michrystridium seems more abundant and Veryhachium less common in the calcitic-shale and limestone subfacies of the Needmore Shale than in the other hystrichospherid-bearing rocks. Cymatiosphaera is less abundant in Beaver Dam black shale than in other rock types. No other statistically valid distribution trends could be observed.

There is no evidence that hystrichospheres can be used to subdivide the Onesquethaw Stage in this region.

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