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Show It has been asserted that the term spina bifula is not correctly applied to the neural spine of the anterior vertebra? in these fishes, because the neural canal is closed ; but in the Molidse this is not the case, and in the Diodontidse the neural canal is open above in the posterior praecaudal region; the anterior bifid spines are in all cases obviously homologous and forming one series with the single neural spines which succeed them, and when the neural canal is closed by a bony roof this must be regarded as a secondary feature, due to the meeting of outgrowths from the base of the neural spine of each side after they have separated. Family 1. T e tro do xt id .e . Praecaudal vertebrae without parapophyses, the first four or five with bifid neural spine and closed neural arch; 110 epipleurals. Pneorbital not ossified ; palatine firmly united to the skull; no distinct bony nasal cavity ; premaxillaries not protractile, united to maxillaries; teeth in the jaws coalescent, in each forming a beak with median suture ; palate toothless; fourth upper pharyngeals present, toothed; lower pharyngeals separate ; interoperculum a long rod, attached to inner face of prseoperculum, sometimes connected with operculum, never with suboperculum. Nostrils various. Four branchial arches, the fourth not bearing a gill, not followed by a slit; pseudobranchiae present; six branchio-stegals, the first a broad plate. Skin naked, usually with movable spines, rarely with bony plates. Caudal peduncle normal. Skeleton well-ossified. Belly very inflatable. Air-bladder present. Many authors have failed to understand the evolution of the nasal organs in this family, as is shown by the wording of their diagnoses, such phrases as " nostrils represented by two solid tentacles on each side," " nostril with a tube," &c. being quite misleading. In the more primitive forms (Lagocephaltis) there are two nostrils on each side, situated in an oval nasal area, which overlies an internal nasal sac, exactly as in Balistes, Triacanthus, &c. From these we pass to fishes (Spheroides) in which the nasal area is raised up into a more or less prominent tubular papilla bearing the two nostrils, whilst the nasal sac is scarcely sunk below the level of the skin, and is in great part represented by the interior of the papilla, on the walls of which are the terminations of the olfactory nerve. By the absorption of the septum between the nostrils at the end of the papilla they become confluent, and we get a circular tube produced terminally into two more or less distinct lips or tentacles, in the more specialized of which the circular tube is short and constricted, so that we have two tentacles, on the inner surface of which are the terminations of the olfactory nerve, united basally. Thus when the nostrils become confluent the interior of the nasal sac is exposed, and in some species of Tetrodon it may be said to be raised above the level of the skin. In Tropidichthys the circular tube has degenerated to an inconspicuous rim with a minute aperture. In 292 MR. C. TATE REGAX OX [Nov. 4, |