Three-dimensionally preserved specimens of Late Ordovician graptolites have been isolated from Vauréal Formation limestone samples collected from Anticosti Island, Quebec. The morphology, astogeny, and systematics of Anticostia macgregorae n.gen., n.sp. are described. These specimens show a new astogenetic pattern (pattern K) described for the first time. The similar glyptograptid species Glyptograptus hudsoni Jackson, Glyptograptus tenuissimus Ross and Berry, and Orthograptus fastigatus Davies all possess a pattern K astogeny. These species, along with Glyptograptus lorrainensis, which possesses the less-derived pattern G astogeny, are included within Anticostia n.gen. Anticostia tenuissima (Ross and Berry) is redescribed and Normalograptus? occidentalis (Ruedemann) is refigured based on their type specimens from coeval rocks in Nevada and Idaho.