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Show 24 PROF. T. H. HUXLEY ON CERATODUS FORSTERI. [Jan. 4, 8. Contributions to Morphology. ICHTHYOPSIDA.-No. 1. On Ceratodm forsteri, with Observations on the Classification of Fishes. By Prof. T. H. HUXLEY, Sec. U.S. [Received January 4, 1876.] Two specimens of Ceratodus forsteri have come into my possession within the last two years. The first was kindly placed at m y disposal by the Secretary of this Society some time ago; but I was unwilling to dissect it until I had a second. This desideratum was supplied by m y friend Sir George MacLeay, who, on a recent visit to Australia, was kind enough to undertake to obtain a Ceratodus for me, and fulfilled his promise by sending m e a very fine and well-preserved fish, rather larger than the first. The first was 32 inches long, the second only 30 inches, though a considerably stouter fish. I need hardly say that I have little to add or qualify in the general description of the exterior structure given by so accomplished and experienced an ichthyologist as Dr. Gunther*. Only in one point do I find m y interpretation of the facts widely discrepant from his; and that is in regard to the position of the external nostrils. Dr. Gunther says, " A s in Lepidosiren, there are two nasal apertures on each side, both being situated within the cavity of the mouth." That anterior nasal apertures should be situated, in any sense, " within the cavity of the mouth " would be so singular a deviation from the otherwise universal rule, that the anterior nares of vertebrated animals are situated outside the mouth, on the surface of the head, that conclusive evidence must be producible before the anomaly can be admitted to exist; and, so far as m y observations go, that conclusive evidence is not only wanting, but the contrary is demonstrable. In Ceratodus, it is easily seen that the anterior nares are not occluded when the mouth is shut by the apposition of the edges of the mandible to the palate. The anterior nares, in fact, lie altogether outside and in front of the contour of the mandibles, on the under concave surface of the anterior part of the head. The median portion of the margin of this region of the head must not be confounded with the upper lip, with which it has nothing to do. The maxillary portion of the upper lip is, in fact, represented only by a fold of the integument, which begins on the outer side of the anterior nostril, and extends back to the angle of the gape, where it passes into the lower lip. The praemaxillary, or internasal, portion of the upper lip is represented by a delicate fold of the integument, disposed in a transverse arch in front of the vomerine teeth, which it separates from the inner boundary of the anterior nares. The outer and posterior portion of the lower lip is produced into a free process, which is folded back against the jaw, and extends for about two thirds of the distance from the angle of the mouth to the symphysis, ending by a rounded free edge. * "Description of Ceratodus," Phil. Trans, pt. ii. 1871. |
