Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/412

size compared with the surviving types of the family. The recent discovery of a specimen in the Lias of Lyme Regis, in which a considerable portion of the anterior structures of a Chimaeroid is preserved, enables me to advance a step in clearing up the mystery which has hitherto shrouded this subject. It was described to me as a new species of shark, showing the dorsal spine in situ, and the upper and lower jaws. Prom a rough sketch of the specimen forwarded with the letter, I was inclined to think, from the peculiar mode of insertion of the spine, that it might possibly belong to a Balistes or a Siluroid fish, certainly that it could not be a shark ; but on examining the specimen itself I found the unmistakable dental apparatus characteristic of the Chimaeroids, surrounded with shagreen; and then perceived that what was described as the upper jaw of a shark could only be a monstrous form of the singular rostral appendage peculiar to the male sex of the Chimaeroids of the present time. The dermal integument has fortunately retained its proper position and outline on the frontal and oral regions, representing a tolerably correct profile of the head. The forehead is characterized by a remarkable prolongation of the skin (Pl. XIII. fig. la), extending six inches beyond the frontal cartilages, and terminating in a hook directed abruptly downwards for more than one inch. This structure is very similar to the prelabial appendage found in the Callorhynchus antarcticus of the present period. Immediately above this projection, and following the outline of its upper margin, is seen what I imagine to be the homologue of the frontal ossicle of the recent male Chimaeroids (1 b). In the latter it exists as a small incurved bone, terminating in a kind of pad covered with minute spines ; but in the fossil it is developed into a formidable rostrum slightly curved at the base, forming a frontal declivity, and then projecting forwards as far as the extremity of the prelabial appendage above described. Its entire length is five inches and a half, of which the anterior two-thirds are straight. The proximal extremity is attached to the head by means of a rounded condyle, which is received in a hollow of the frontal cartilage — an arrangement which allows of a limited amount of motion in the vertical plane. The underside of the rostrum is thickly beset with tubercles carrying recurved central spines, not unlike the dermal tubercles of some of the recent Raiidoe. Similar spine-bearing tubercles, seated on the upper surface of the nasal prolongation, are opposed to the former, so that a fragmentary specimen of this portion of the fish might easily be mistaken for parts of an upper and lower jaw. The tubercles extend in diminished size and numbers along the entire under surface of the organ. The upper surface was covered by coarse-grained shagreen, which probably invested also the sides ; but it has perished in these parts, and the coarse fibrous structure of the bone is displayed. About one inch behind the insertion of the frontal spine the orbit is seen. This is of large size, measuring one inch in diameter. Two inches behind the orbit, and in close proximity to the occipital region, the dorsal spine (lc) is situated. Before, however, entering upon the description of this organ, it will