. Bonner zoologische Monographien. Zoology. 101. Fig. 44: Branchiostegal rays and relationships with ceratohyal and epihyal in young specimens. — A: Loricarichthys sp. (ANSP 131612); B: Callichthys callichthys (KU 13722). brl—4: branchiostegal rays 1—4; ch: ceratohyal; dh: dorsal hypohyal; eh: epihyal. b) Hypohyals: Dorsal and ventral hypohyals (Fig. 27A—B) have similar size and shape in diplomystids. They differ slightly in ictalurids, and the ventral hypohyal is rudimen- tary in Nematogenys, Heptapterus, and also in Eutropiichthys (Tilak 1961). No ventral hypohyal exists in trichomycterids.
. Bonner zoologische Monographien. Zoology. 101. Fig. 44: Branchiostegal rays and relationships with ceratohyal and epihyal in young specimens. — A: Loricarichthys sp. (ANSP 131612); B: Callichthys callichthys (KU 13722). brl—4: branchiostegal rays 1—4; ch: ceratohyal; dh: dorsal hypohyal; eh: epihyal. b) Hypohyals: Dorsal and ventral hypohyals (Fig. 27A—B) have similar size and shape in diplomystids. They differ slightly in ictalurids, and the ventral hypohyal is rudimen- tary in Nematogenys, Heptapterus, and also in Eutropiichthys (Tilak 1961). No ventral hypohyal exists in trichomycterids. I interpret the condition of Diplomystidae as primitive, and hypothesize a trend toward loss of the ventral hypohyal in siluroids. c) The articular facets between the ceratohyal and epihyal are smooth and weakly join- ed in Diplomystidae "(Fig. 27C) and Trichomycteridae. The articulation between those bones is produced by a dentated suture in Ictalurus and Nematogenys', in the latter, both interdigitating surfaces become partially fused in the largest specimens. I interpret the last condition as derived within siluroids. Opercular series: Diplomystids lack a subopercle, as do most catfishes. The presence of one to three suprapreopercles in diplomystids is shared with other siluroids such as ictalurids, nematogenyids, pimelodids, other ostariophysans, and some primitive teleosts (Nybelin 1974). The preopercle of diplomystids lacks a ventral limb, as in other siluroids. Fink & Fink (1981) state that the interopercle is shortened considerably on an antero-posterior axis, so the interopercle is a short triangular bone in siluroids. A short slightly triangular bone is present in several siluroids, including diplomystids, ictalurids (Lundberg 1982), hypophthalmids (Howes 1983 b), and Nematogenys (Arratia et al. 1978). A large elongate bone is present in trichomycterids (Arratia et al. 1978, Arratia & Menu Marque 1984); thus, this feature cannot be con- sidered as
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