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Show 54 DR. W. G. RIDEWOOD ON THE CRANIAL [May 3, be restricted in the main to primitive features. There is no doubt that the Elopidse are the most archaic of existing Teleosteans, and that the Albulidae are in few respects more highly specialised ; but the study of the skull does not show any direct affinity between the two families. There is no specialised character common to both. Such resemblances as exist between them are explicable by the fact that neither has departed to any great extent from the ancestral group from which all the Teleostean fishes sprang ; and there is no evidence (from the study of the skull) that the divergence of the two families from a single one occurred at any considerable height above the root of the phylogenetic tree. In the presence of conal valves of the heart other than those at the junction of the conus with the ventricle (see Boas, Morph. Jahrb. vi. 1880, p. 528), Albula exhibits a character common in Ganoid and still lower fishes, but not possessed by any other living Teleostean ; while in the possession of a median jugular or gular plate Elops and Megalops exhibit a resemblance to the Ganoid Amia which is not shared by any other Teleostean fish. The Elopidse were abundant in Cretaceous times, and some of the extinct forms would seem to be more specialised than the living Elops and Megalops, since they exhibit a reduction in the size of the jugular plate (Thrissopater and Spanioclon) and a separation of the two parietal bones (Rhacolepis, Thrissopater, Spcmiodon, and others). (See Smith Woodward, Brit. Mus. Cat. Foss. Fish, iv. Introduction, p. vi.) There is no instance among Teleosteans of a paired vomer such as occurs in Amia and its allies, but it is worthy of note, perhaps, that in Elops, and to a lesser extent in Megalops, the vomerine teeth are disposed in two patches, right and left. Of the characters common to the skulls of the Elopidse and the Albulidse may be mentioned the small size of the parietal bones and their meeting in the median line; the roofing of the posterior temporal fossae ; the presence of subtemporal fossse ; the presence of opisthotic, basisphenoid, and orbitosplienoid bones, an upper and lower hypohyal on each side, and an ossified first pharyngobranchial ; the distinctness of the endosteal articular from the ectosteal articular, and the fusion of the angular bone with the latter; and the presence of teeth on the dentary, premaxillary, entopterygoid, and parasphenoid bones. Teeth occur on the vomer and palatine in Elops, Megalops, and Albula, but not in Bathythrissa. Minute denticles occur on the surface of the ectopterygoid in Elops and Megalops, but there are none in Bathythrissa and only two or three small teeth at the front of the ectopterygoid in Albula. The mouth in the Albulidse is reduced in size, and its upper border is formed by the pre-maxillae alone, the maxilla? being toothless, whereas in the Elopidfe the upper border is supported by both premaxillse and maxillfe, and both bear teeth. There are two surmaxillfe on each side in the Elopidse, and one in the Albulidfe. The mandibular suspensorium (hyomandibular and quadrate) is slightly tilted forwards in Elops; in Albula it is strongly rotated |