Dictionary of Ichthyology  

interopercle = the paired dermal bone of the lower gill cover below the horizontal arm of the preopercle and in front of the subopercle. Connected to the mandible by a ligament. Absent in Lepisosteus and Siluridae.

Hyoid and opercular apparatus of Gadus, B = branchiostegals, E = os entoglossum, H = hyoid, HM = hyomandibula, I = interoperculum, O = operculum, P = preoperculum, S = suboperculum, from Kingsley's "Textbook of Vertebrate Zoology, 1906. Photograph by Brian W. Coad.

Canadian Museum of Nature