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Show 78 DR. \V. G. RIDEWOOD OX THE CRANIAL [May 3, Roccus (Proc. Wash. Acad. Sci. iii. 1901, pi. lxiv.), allude to the hypohyal as the basihyal. Owen (Anat. of Vert. i. 1866, pp. 106 & 124), it is true, used the word basihyal in this sense, and was followed by Giinther (‘ Study of Fishes,' 1880, p. 58) and others; but the homology between the glossohyal of the Teleostean and the basihyal of the Elasmobranch is now so firmly established that there is no justification for reviving an erroneous terminology. What is more incomprehensible than the retention of an obsolete application of the term basihyal is the fact that Starks, while calling the hypohyals the basihyals in 1901 (I. c.), designates them hypohyals in 1898 and 1904 (Proc. Calif. Acad. Sci. (3) i. 2, 1898, pi. xxiii. fig. 8, Sebccstolobus; and Proc. U.S. Nat. Mus. xxvii. 1904, p. 603, Berycoid fishes). Most writers are in agreement as to the application of the terms epihyal and ceratohyal, but Allis has adopted an unusual nomenclature which appears to have very little to recommend it beyond the fact that it serves to locate the main jointing of the hyoid arch between the epi- and cerato-elements, as occurs in the branchial arches ; he regards the epihyal as a part of the ceratohyal (which is, according to his view, a double ossification), and calls the interhyal the epihyal (Journ. Morph, xii. 3, 1897). The glossohyal or basihyal varies greatly in size, being largest in Hyodon, and extremely reduced in Engraulis and Coilia. There is no separate glossohyal in the Mormyridae; it is either wanting, or is fused with the first basibranchial. An endosteal glossohyal is frequently present in addition to the ectosteal and usually dentigerous bone (e. g., Albula, Chirocentrus, Megalops), but in such forms as Heterotis, Osteoglossum, Chatoessus, Clupea, and Alepocephalus the cartilage remains unossified. The dentigerous plate which covers the first, second, and third basibranchials is readily removable in Arapaima, but in most cases it is fused with the second, and overlaps the hinder part of the first basibranchial and the anterior part of the third basibranchial (e. g., Clupea, Chirocentrus, Engraulis). In Hyodon it is fused with the third as well as with the second basibranchial, and in Albula it is fused with all three basibranchials, and overlaps, but is not fused with, the posterior half of the glossohyal. It is much reduced in size in Chatoessus, in which it is edentulous ; and in Gonorhynchus it is confined to the second basibranchial. In Dussumieria each of the three basibranchials has its own dentigerous investing bone. There is in most cases also a much smaller dentigerous bone covering the plate of cartilage that represents the fourth and fifth basibranchials. The first basibranchial is unossified in Heterotis, Notopterus, and Gonorhynchus. The second basibranchial is remarkably long in Engraulis, and the parallelism of the first and second cerato-branchials is much disturbed in consequence. In Chanos the anterior ends of the fourth and fifth ceratobranchials are separated by a narrow, elongated tract of cartilage; in Alepocephalus and Chatoessus the anterior ends of the third and fourth cerato- |
