. Bulletin of the British Museum (Natural History) Geology Supplement. ESPECIALLY MYCTOPHOIDS 215 hypohyals. Fifteen branchiostegal rays occur on the hyoid arch, all being of similar size and shape. Eight are present on the ceratohyal and 7 on the epihyal. Branchial arches. The basibranchials are fused into a single median elongate element, supporting three pairs of hypobranchials. Five discrete ceratobranchials are present, the first two of which bear toothed gill-rakers. Gill-rakers are absent on the third and fourth ceratobranchials but teeth are still present. The fifth cerato- branchial i
. Bulletin of the British Museum (Natural History) Geology Supplement. ESPECIALLY MYCTOPHOIDS 215 hypohyals. Fifteen branchiostegal rays occur on the hyoid arch, all being of similar size and shape. Eight are present on the ceratohyal and 7 on the epihyal. Branchial arches. The basibranchials are fused into a single median elongate element, supporting three pairs of hypobranchials. Five discrete ceratobranchials are present, the first two of which bear toothed gill-rakers. Gill-rakers are absent on the third and fourth ceratobranchials but teeth are still present. The fifth cerato- branchial is the only remaining ossification of the fifth arch. It is enlarged into a prominent tooth plate, the inferior pharyngeal bone. Weitzman (1967 : 530) finds a small cartilaginous fifth epibranchial, ligamentously attached to the fifth cerato- branchial. Four epibranchials are present and, like the ceratobranchials, the first two bear toothed gill-rakers but the third and fourth simply bear teeth. There are four pharyngobranchials ; the first is small and attaches to the parasphenoid. Pharyngobranchials 2, 3 and 4 are fused into a tooth plate which opposes the inferior pharyngeal bone. Weitzman (1967 : 530) reports that a fifth pharyngeal tooth plate occurs in Aulopus, but he goes on to suggest that by its morphological relation- ships this tooth plate may actually belong to the fourth arch. Nelson (1967 : 286) indicates that Aulopus has a fifth tooth plate as a separate element. Pectoral girdle and fin. The pectoral girdle is shown in medial view in Text-figure 91. The supratemporal is composed of transverse and longitudinal limbs. The transverse limb lies on the postero-dorsal regions of both the pterotic and parietal forming a part of the roof of the post-temporal fossa (Text-fig. 86). This extension contains the supratemporal sensory canal. The longitudinal limb is the shorter of sea v. pel. Fig. 91. Aulopus filamentosus. Pectoral girdle of the left side in medial view.
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