Dictionary of Ichthyology  

auditory capsule = cartilaginous skeleton about the inner ear in Elasmobranchii, a chondral skeleton in bony fishes comprised of the prootic, opisthotic (or its replacement), intercalar, epiotic (or exoccipital), sphenotic, pterosphenoid and basipshenoid as walls and floor with the parietals and frontals as the roof.

Shark skull, a = auditory capsule, b = basibranchial, c = keratobranchial, e = epibranchial, g = gill cleft, h = hyoid, hm = hyomandibula, l = labial cartilages, m = mandible (Meckel's cartilage), o = olfactory capsule, p = pharyngobranchial, pq = pterygoquadrate, r = rostrum, s = spiracle, 2, 5 = exits of second and fifth nerves, I-V = branchial arches., from Kingsley's "Textbook of Vertebrate Zoology, 1906. Photograph by Brian W. Coad.

Canadian Museum of Nature