. Bulletin of the British Museum (Natural History) Zoology. 140 G. J. HOWES & AYANOMIYA FUMIHITO exo. Fig. 6 Neurocrania in posterior view of A, Belodontichthys dinema (LILI 89008); B, Ompok bimaculatus (:171-8); C, Wallago leeri (:203). In Belodontichthys, the canal branch extends postero- laterally, having a reversed orientation relative to that of other silurids but nonetheless still retains the lateral pore opening in the same position, viz midway along the edge of the frontal and above the orbit, the opening interconnecting with those of the sphenotic and infraorbit
. Bulletin of the British Museum (Natural History) Zoology. 140 G. J. HOWES & AYANOMIYA FUMIHITO exo. Fig. 6 Neurocrania in posterior view of A, Belodontichthys dinema (LILI 89008); B, Ompok bimaculatus (:171-8); C, Wallago leeri (:203). In Belodontichthys, the canal branch extends postero- laterally, having a reversed orientation relative to that of other silurids but nonetheless still retains the lateral pore opening in the same position, viz midway along the edge of the frontal and above the orbit, the opening interconnecting with those of the sphenotic and infraorbital canals (see above and Fig. 2A). The lateroposterior orientation of the canal branch in Belodontichthys, Ompok and Wallago we consider as a shared derived state (see further discussion on p. 155). In Belodontichthys the sphenotic is separated dorsally from the frontal by the lateral ethmoid, but the bones are in contact ventrally (Figs 2A, B). In other silurids examined the entire anterior margin of the frontal contacts the lateral ethmoid, a condition (first noted by Regan, 1911) not encountered elsewhere in siluroids and one considered synapomorphic for the Siluridae (Bornbusch, 1988; 1990). Kobayakawa (1989) figures the frontal in Silurus mento. S. cochinchinensis. S. grahami and S. microdorsalis as forming the lateral orbital border of the cranium, at least dorsally; if this is so, then the distribution of this character is incongruent with others shown in her cladogram of relationships. Bornbusch (pcrs. comm.) notes that there is variability within silurid taxa with respect to the degree of dorsal exposure of the frontal along the orbital margin. The raised lateral border of the pterotic in Belodontichthys is a feature shared with Ompok. In both those taxa the sensory canal comes to lie along the 'medial' surface of the elevated border (Fig. 6A, B). In Silurus and Wallago (Fig. 6C) the pterotic border is also slightly raised but in other genera the border and its associa
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