Periptychus was an unusual mammal that combined a number of rather specialized dental, cranial, and postcranial features with a relatively generalized skeletal structure.

The morphology of the rostrum of this animal was very similar to that found in related genera such as Carsioptychus or Ectoconus; the snout was not elongated as in other condylarths such as Arctocyon, but it was longer than that of pantodonts such as Pantolambda.

In lateral view, the dorsal surface of the skull of Periptychus was relatively flat compared to the more domed morphology found in Pantolambda.

The maxilla was characterized by an unusual pitted surface, just above the tooth row; these holes, concentrated mainly above the premolars and around the infraorbital foramen, varied in shape and size: some were circular and others ovoid, and did not exceed 0.7 millimeters in diameter.

The dental enamel was strongly crenulated with well-aligned ridges, typical of all periptychids but reaching their maximum development in Periptychus.

Periptychus was first described by Edward Drinker Cope in 1881, based on fossil remains found in New Mexico in deposits dating to the Middle Paleocene.

The fossils were very fragmentary including a part of a jaw with teeth and belonging to a juvenile specimen, which Cope did not recognize as such and assigned it to Creodonta.

The postcranial skeleton of Periptychus indicates that this animal was plantigrade, adapted to move slowly over the ground; it was also capable, on occasion, of making rapid movements.

The flexor and extensor muscles in the hands and fingers were highly developed, indicating that this animal was probably capable of climbing and digging.