. Bulletin of the British Museum (Natural History) Zoology. . maxillary process via tendinous tissue. The sensory canal runs through the ventral part of the lachrymal. The other infra- orbitals are narrow and the sensory canal runs along their dorsal rim. The 5th infraorbital is reduced to a bony tube which extends dorso-posteriorly and does not contact the lateral process of the sphenotic. There are thus large gaps between the 5th infraorbital and the sphenotic, and the 5th infraorbital and the opercular process. Almost all of the dilatator operculi muscle is exposed. There is also a wide gap
. Bulletin of the British Museum (Natural History) Zoology. . maxillary process via tendinous tissue. The sensory canal runs through the ventral part of the lachrymal. The other infra- orbitals are narrow and the sensory canal runs along their dorsal rim. The 5th infraorbital is reduced to a bony tube which extends dorso-posteriorly and does not contact the lateral process of the sphenotic. There are thus large gaps between the 5th infraorbital and the sphenotic, and the 5th infraorbital and the opercular process. Almost all of the dilatator operculi muscle is exposed. There is also a wide gap between the pterotic and dorsal border of the operculum and the levator operculi is well-developed. The condition of the circumorbitals in all species of Onychostoma and Scaphesthes is the same as described for O. sima. In Varicorhinus beso (Fig. 12) the lachrymal is also a deep pentagonal bone but the sensory canal runs centrally through the bone; the anterior part of the sensory canal runs close to the bone's anterior border. The 2nd and 3rd infraorbitals are shallow but the 4th and 5th infraorbitals are deep. In some species of Varicorhinus, V. ruwenzorii (Fig. 13a) and V. macrolepidotus, the 4th and 5th infraorbitals are apparently fused (in some specimens of V. beso both the 4th and the 5th may be present on one side only). The upper infraorbital is never reduced and contacts the lateral process of the spheno- tic and the opercular process. The dilatator operculi muscle is almost covered completely by the infraorbital, and the upper gap between the pterotic and the opercular border is very narrow. The shape of the lachrymal is variable in the barbins (Howes, 1987) and it is difficult to evaluate it as a phylogenetic character. In most barbins (Fig. 13a—j) the 4th infraorbital is not reduced and the 5th infraorbital is never reduced to only the sensory canal and it always contacts the lateral process of the sphen- otic. Cyprinion and Semiplotus (Fig. 13i,j) both pos
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