OCR Text |
Show 1904.] OSTEOLOGY OF THE ELOPID.E AND ALBULHLE. 71 prehension at all. A similarly constituted mouth occurs in the Moimyridae. The right and left premaxillse of Mormyroid fishes are fused, and the suture obliterated (except in Gymnarchus). A similai condition is said to exist jn Pantodon. In Chanos, Chatoessus, and Gonorhynchus the premaxilla alone bounds the gape above, and is devoid of teeth. The exceptional, and apparently useless, backward prolongation of the maxilla of Coilia is a well-known feature of that genus, and claims but a passing mention. There are two surmaxillte above each maxilla in Coilia, En-grauhs, Clupea, Dussumieria, Chirocentrus, Elops, Megalops, and Alepocephalus, one in Chatoessus and Albula, and none in Chanos, Arapaima, Heterotis, Osteoglossum, the Mormyridae, Hyodon, A otopterus, and Gonorhynchus. Two surmaxilke are present in the Mesozoic -families Pholidophoridse. Leptolepidas, and Oligo-pleuridse. Mandibular Series.-The angular bone is distinct in Arapaima, Heterotis, Osteoglossum, Notopterus, and most Clupeoids, but not in Coilia and Engraulis, nor in the Mormyridse, Hyodon, Albula, Elops, uml Megalops. In Notopterus the angular is a much larger bone than usual. The endosteal and ectosteal parts of the articular bone are distinct and separable in Arapaima; and, according to Hay (Zool. Bull. ii. 1, 1898, p. 37), they are also distinct in the Cretaceous genus Xiphactinus. He shows that Cope's interpretation of the mandibular bones of this form was entirely erroneous. Since the remark of Owen's (Anat. of Vert. i. 1866, p. 123), that in Arapaima there is a superadded bony piece answering to the surangular of Reptiles, is credited by so recent a writer as Smith Woodward (Brit. Mus. Cat. Foss. Fish. iii. 1895, p. xix), it may be well to point out that this superadded bone, marked 29 a in Owen's fig. 88, is but the endosteal articular displaced. In Gymnarchus, Hyodon, Albula, Elops, and Megalops the endosteal and ectosteal components of the articular would probably separate with prolonged maceration, for the suture between them is clearly visible, but I was unable to submit the material in hand to such treatment. As a rule the suture is not visible in Teleostean fishes. In some forms the posterior part of the surface for the articulation with the condyle of the quadrate is formed by the angular, the part of the angular bone concerned having a distinctly endosteal appearance. Such is the case in Gonorhynchus, Arapaima, Albula, Megalops, Elops, Gymnarchus, Hyodon, and Heterotis, but in Osteoglossum, Notopterus, and the Clupeidse the articular facet is formed by the endosteal articular alone. In Notopterus and the Clupeidc© the angular bone has the appearance of an ectosteal bone. Except in a few forms (e.g.,Arapaima, Petrocephalus, Engraulis, Chatoessus, Dussumieria) there is a distinct bone lying usually in front of the endosteal articular and on the inner (lingual) surface |