. Bulletin of the British Museum (Natural History). nective tissue body (the 'nodule') which is intermediate between the Halosaurus type and that of Notacanthus (see above, and Figs 20 & 21). The relationships of the maxilla with the pyriform body in Lipogenys can also be considered as intermediate between the other two types. Thus, contrary to the view of McDowell (1973 : 6 & 131) cited on p. 90 above, I would consider that an autopalatine is present in halosaurids, notacanthids and lipogenyids, and that the nodule of connective tissue (or connective tissue and cartilage) present near
. Bulletin of the British Museum (Natural History). nective tissue body (the 'nodule') which is intermediate between the Halosaurus type and that of Notacanthus (see above, and Figs 20 & 21). The relationships of the maxilla with the pyriform body in Lipogenys can also be considered as intermediate between the other two types. Thus, contrary to the view of McDowell (1973 : 6 & 131) cited on p. 90 above, I would consider that an autopalatine is present in halosaurids, notacanthids and lipogenyids, and that the nodule of connective tissue (or connective tissue and cartilage) present near the anterior tip of the auto- palatine is a neomorphous structure (probably characteristic of these three families alone) which evolved as part of the peculiar jaw mechanisms found in these fishes. That the function of the connective tissue nodule differs in notacanths (including lipogenyids) and halosaurs is perhaps indicated by its different relationships with the upper jaw and pterygoid arch in the two groups (cf. Figs 20 & 21). DCtnod TA1P -I-A2P. ApPmx 3mnn Fig. 21 Notacanthus bonapartei. Figure to show ethmo-palato-maxillary relationships, viewed obliquely from a ventro-anterior position (right side); the various elements are depicted in situ. Specimen BMNH : 33. Since the primitive elopomorphs Albula and Pterothrissus have a double contact between the palatopterygoid arch and the skull (anteriorly with the ethmoid cartilage, and somewhat more posteriorly with the lateral ethmoid), the single contact in halosaurs and lipogenyids must be considered a derived condition, and the complete loss of direct contact in notacanths (see above, p. 92) a further specialization. Lateral line scales In all halosaurids, notacanthids and lipogenyids, the canal-bearing lateral line scales on the flanks are highly specialized. The sensory canal is a soft, membranous tube supported by a pair of flanges developed from the scale itself (see McDowell, 1973, for a detailed and ill
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