. Bulletin of the British Museum (Natural History), Geology. 152 PALAEONISCOID FISHES AND THE CHONDROSTEI The unpaired fins. Both dorsal and anal fins are triangular and of similar size with between forty and forty-five rays. The articulations of the rays in both fins are so close that the joints of the base of the fins look most scale-like. The fin rays are smooth apart from a single longitudinal furrow. The caudal fin is heterocercal, inequilobate and deeply cleft. The squamation. The scales of the flank are slightly higher than broad and at the deepest point of the body number around twenty
. Bulletin of the British Museum (Natural History), Geology. 152 PALAEONISCOID FISHES AND THE CHONDROSTEI The unpaired fins. Both dorsal and anal fins are triangular and of similar size with between forty and forty-five rays. The articulations of the rays in both fins are so close that the joints of the base of the fins look most scale-like. The fin rays are smooth apart from a single longitudinal furrow. The caudal fin is heterocercal, inequilobate and deeply cleft. The squamation. The scales of the flank are slightly higher than broad and at the deepest point of the body number around twenty-two rows. They possess a distinct peg and socket articulation and in proportion to body size the scales are large. The ornamentation is most distinct consisting of prominent ridges of enamel (Text-fig. 3). The ridges follow the postero-ventral margin and also the dorsal margin. There is a triangular portion posteriorly where short, pointed, overlapping tubercles pass back towards the hind margin which is pectinated. There are three large ridge scales in front of the dorsal fin, and the ridge scales of the axial lobe start immediately behind the dorsal fin. Scale structure. The general structure of the scale can be seen from Text-fig. 4. Aldinger (1937 : 212) has already pointed out the similarity of the scale structure to that seen in Elonichthys. The canal plexus of the dentine layer is composed of horizontal and radial canals (vascular). The horizontal canals bear tree-like dentine tubules. The radial canals penetrate obliquely through the bony lamellae from the scale margins, sending feeder branches upwards to connect with the horizontal canals. Thus the radial canals are for the most part at a much deeper level than the horizontal canals. A few canals (canals of Williamson) penetrate upwards from the centre of the base of the scale to connect with both the radial canals and the horizontal. Fig. 4. Gonatodus punctatus (Agassiz). Dorso-ventral cross section throug
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