Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/283

 matrix, enveloped both without and within with a coat of ganoine on those parts not subservient to molendular attrition. The occurrence of these two pairs of anterior molars in the lower jaw accords with the unusual elongation of the premaxillary or incisor teeth. Were the mandibular plates united at the symphysis (as in all the typical Chimaeroids), the premaxillaries would have overlapped them, and, having no opposing whetstone to work upon, would have continued growing from the basal pulp-cavity (like the distorted incisor of a Rodent) until they would have been an incumbrance to the fish rather than auxiliaries in providing for its sustenance ; but, by the anterior extension of the mandibular dental apparatus, provision is made for the opposition of the upper and lower teeth, by which a permanent prehensile apparatus is secured for seizing and tearing the prey preliminary to the mastication which it would subsequently undergo between the crushing surfaces of the hinder molar teeth.

Besides the dental machinery which has been described, the specimen comprises other features no less singular. Attached to the upper edge of the maxillary plates, and extending three inches on either side of the mesial frontal line, there is seen a broad horizontal plate with a sinuous outline, which suggested to the finder the semblance of the wings of a Bat. It appears to be composed of a cartilaginous material, without any trace of osseous structure, and with no sutures or other demarcations on its surface. The lateral extremities are rounded ; and that on the right side is overlapped by a plate of a harder material, studded over with a tubercular pattern very similar to that common on the cranial bones of some of the secondary Ganoid Fishes. This plate is semielliptic, having the base, which is directed forwards, concave, and the outer curve armed with two strong dermal spines. The inner curve has the appearance of having been united by a squamosal suture to an adjoining plate ; and this leads to the supposition that the cranial cartilage was entirely cased by similar plates, as in the recent Acipenser. It is also highly probable that the orbit was situated beneath the concavity in what may therefore be considered the supraorbital plate, protected by the spines projecting from the margin of the plate (P1. VIII. o). On either side of the frontal mesial line, and superimposed upon the cartilage, is a cylindrical osselet one inch in length. These bones have their anterior extremities coincident with the bases of the premaxillary teeth, affording to them support, and perhaps attachment for muscles connected with the masticatory function. Dr. Gunther informs me that he has found a pair of nasal cartilages in a similar position in the recent Chimoera monstrosa. Both these and the cranial plate must be composed of a more indestructible material than ordinary cartilage, which is rarely found in the fossil state.

Taking all the characters of this singular specimen into consideration, it will, I think, be conceded that this Fish is a novelty in palaeichthyology of no ordinary interest. The form of the head, extended in the horizontal instead of the vertical plane, suggests the strange appearance of a Zygoena, but covered with hard plates like a Sturgeon. The maxillary teeth most resemble those of Callorhynchus, s 2