. Catalogue of the fossil fishes in the British Museum (Natural History) ... Fishes, Fossil. CHONDROSTEID^. 25 the anterior rays of each fin gradually increasing in length to an acumination. Pelvic fins remote, the dorsal opposed to this pair; caudal fin forked, nearly equilobate. Scales absent, except on the upper caudal lobe where they are thick and rhombic, invested with ganoine; caudal Moral scales large, with ganoine. Nothing is known of the ossifications in the chondrocranium of Chondrosteus, but many specimens exhibit the chief membrane- bones. The parietals (figs. 3, 4, jp.) are longer
. Catalogue of the fossil fishes in the British Museum (Natural History) ... Fishes, Fossil. CHONDROSTEID^. 25 the anterior rays of each fin gradually increasing in length to an acumination. Pelvic fins remote, the dorsal opposed to this pair; caudal fin forked, nearly equilobate. Scales absent, except on the upper caudal lobe where they are thick and rhombic, invested with ganoine; caudal Moral scales large, with ganoine. Nothing is known of the ossifications in the chondrocranium of Chondrosteus, but many specimens exhibit the chief membrane- bones. The parietals (figs. 3, 4, jp.) are longer than broad and comparatively small; both these and the large frontals (/.) meeting at the middle line in a slightly wavy suture, without any inter- posed elements or vacuities. The squamosals (sq.) are larger than the parietals, extending as far forwards as the latter; the post- frontals () are relatively very small. ISTo cranial bones have been recognized in advance of the frontals, and the extent of the rostrum is thus undetermined. Cheek-plates are also almost wanting, only one suborbital (figs. 3, 5, so.) being observed, bearing an upward process ascending towards the postfrontal. A series of five supratemporal plates (fig. 4, ), of which the three inner- most are relatively small, occurs along the occipital border. The hyomandibular (figs. 3, 6, hm.) is shaped as in modern Sturgeons, but apparently ossified as far as its lower extremity; and a sym- plectic must have been present, although it is doubtful whether this was ossified in any part. The pterygo-quadrate arcade exhibits only two ossifications on each side, one being a large expanded Fig. Profile of head of Chondrosteus acipenseroides, restored (after Traquair). j., jugal. Other letters as in figs. 4, 5. element (PI. I. fig. 3, jot.) of pterygoid nature, and the other a small V-Shaped bone (pi.) articulated with the maxilla, which Sheathing the arcade is may be either palatine or Please
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