'24 PROF. T. H. HUXLEY ON CERATODUS FORSTERI. [Jail. 4, 



8. Contributions to Morphology. Ichthyopsida. — No. 1. 

 On Ceratodus forsteri, with Observations on the Classifi- 

 cation of Fishes. By Prof. T. H. HuxleYj Sec. K,.S. 



[Eeceived January 4, 1876.] 



Two specimens of Ceratodus forsteri have come into my posses- 

 sion within the last two years. The first was kindly placed at my 

 disposal by the Secretary of this Society some time ago ; but I was 

 unwilhng to dissect it until I had a second. This desideratum was 

 supplied by my 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 me 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 tliat 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. Giinther*. Only in one point 

 do I find my interpretation of the facts widely discrepant from his ; 

 and that is in regard to the position of the external nostrils. 



Dr. Giinther says, "As 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 verte- 

 brated animals are situated outside the mouth, on the surface of the 

 head, that conclusive evidence must be producible before the ano- 

 maly can be admitted to exist ; and, so far as my 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 oc- 

 cluded 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 por- 

 tion 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. 



