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Show 492 DR. W. G. RIDEWOOD ON THE CRANIAL [Dec. 13, Fregatte Novara, Zool. i. 1869, Fisclie ; Cope, Trans. Amer. Pliil. Soc. n.s. xiv. 1871, p. 455 ; Gill, I. c. p. 17 ; Smith Woodward, Brit. Mus. Cat. Foss. Fishes, iv. 1901). Their justification appears to lie mainly in the fact that Chirocentrus possesses in its intestine a spiral valve which is not present in Clupea and its allies (Valenciennes, I. c. p. 160 and pi. 565), in the absence of cseca (ibid. p. 162), and in the presence of a pseudobranch in Chirocentrus and its absence from most Clupeoids (Muller, Abliandl. Akad. Wiss. Berlin, 1844 (1846), p. 191). The only craniological differences worth mentioning are the considerable depth of the posterior temporal groove of Chirocentrus, the small size of the orbitosphenoid, the firm union between the premaxilla anti maxilla (Valenciennes, I. c. pp. 150, 152, and 154), the more or less complete concealment of the symplectic (Boulenger, Ann. Mag. Nat. Hist. (7) xiii. 1904, p. 164), the bony nature of the first pliaryngo-branchial, and the absence of a spicular bone. The value of the evidence of the last two items is certainly not great, for except when (as in Flops) both ossified first pliaryngobrancliial and spicular bones are present, it is not possible to deny absolutely that what appeal's to be the first pharyngobranchial bone is not the spicular bone which has become shortened and thickened and more forwardly directed than usual. The resemblances existing between the skeleton of Chirocentrus and that of such extinct forms as Fortheus, Ichthyodectes, and Saurodon, which attained their maximum development in Cretaceous times, suggest that the former genus is a survival of an ancient type (see Smith Woodward, I. c. p. vii) ; but the teeth of the existing Chirocentrus are not lodged in distinct sockets as are those of the Saurodontida\ As regards Chanos, the evidence of the skull favours the view of separating the genus from the Clupeida?, and of according it a family rank. Chanos has experienced a variety of treatment at the hands of taxonomists. It was first regarded as a species of Mugil (Forskal, Desc. Anim. 1775, p. 74 ; Gmelin, Syst. Nat. Linn. i. 3, 1788, p. 1398), and later as a species of Leuciscus (Gray and Richardson, Dieffenbacli's " Travels in New Zealand,' 1843, ii. p. 218). Valenciennes (Hist. Nat. Poiss. xix. 1846) placed it with Gonorhynchus among the " Malacopterygiens intermediaires entre les Brochets et les Clupes." Gunther (Brit. Mus. Cat. Fishes, vii. 1868) placed it in a. group " Chanina" of the family Clupeida1, and Kner (Reise der Fregatte Novara, Zool. i. 1869, Fische), Cope (Trans. Amer. Phil. Soc. n. s. xiv. 1871, p. 455), and Gill (Smithson. Miscell. Coll. No. 247, 1872, p. 17) separated it from the Clupeida! and placed it in a family of its own. The inclusion of Chanos within the family Albulidae, a step which has commended itself to so experienced an ichthyologist as Smith Woodward (Brit. Mus. Cat. Foss. Fishes, iv. pp. 60 and 64), is justified in so far as the posterior temporal fossa? are roofed over, which is not the case in any other Clupeoid fishes, and in the presence of a well-marked lateral temporal groove, partially roofed |