A limestone stratum, within the undifferentiated West Castleton-Hatch Hill formations of the Taconic sequence in Northwest Dutchess County, New York, has yielded a small collection of agnostid and ptychoparioid trilobites. The agnostids are Pseudagnostus sp.; the ptychoparioid trilobites are Cheilocephalus sp., Dunderbergia sp., Dytremacephalus sp., Glyptometopsis spp., Quebecaspis cf. Q. hemispherica, and Tholifrons sp. The association of genera in this fauna is characteristic of the Pterocephaliid biomere; the fauna is therefore late Dresbachian and is the only fauna of this age known from the Taconic sequence. The fauna has affinity with Dresbachian faunas of the Conococheague and Frederick limestones of the central Appalachians; the Gorge Formation of northwestern Vermont; boulders in conglomerates in Quebec and in western Newfoundland; and Alaska. The stratigraphic context of these faunas suggests they are shelf margin or slope faunas.--Modified journal abstract.