The narrowmouthed catshark was first formally described as Scyllium bivium in 1838 in the book Systematische Beschreibung der Plagiostomen written by Johannes Peter Müller and Friedrich Gustav Jakob Henle in which they ascribe the name to the Scottish surgeon and zoologist Andrew Smith.

Smith gave the type locality as the Cape of Good Hope when he published the name in the South African Quarterly Journal of October 1831.

This fish displays heterodont dentition; the mouth is long in both sexes, but is longer and narrower in males, with teeth that are twice the height of those of females.

[6] The narrowmouthed catshark is endemic to the coasts of South America, between latitudes 23° S and 56° S.[7] In the southwestern Atlantic Ocean its range extends from southern Brazil, southwards to the Beagle Channel and in the southeasterly Pacific Ocean, southwards from northern Chile.

In the Beagle Channel in the summer it has been found to feed almost exclusively on the squat lobster Munida gregaria, but in other places its diet is more varied.