Previously unstudied and earlier-known specimens have revealed the wide cephalic doublure and median ventral suture in Stenopilus; the hypostome is unknown but was probably natant. The cranidium of S. pronus differs from that of the type species S. intermedius in its greater length and convexity; the pygidium is known from rare complete specimens. These two species are present in Quebec, Newfoundland, and Vermont. They are differentiated from Leiocoryphe, which also had a highly effaced cephalon. Relationships remain problematic between these two genera and others currently placed in Plethopeltidae. An enrolled specimen of S. pronus is refigured and the anatomy and mode of life considered as that of a vagrant benthic animal rather than one that lived in a burrow as previously thought.