1872.] EGEPvTOir PEOGNAXnODUS GUiS^HEEI. 235 



matrix, enveloped both without and within with a coat of ganoine 

 on those parts not subservient to molendular attrition. The occur- 

 rence of these two pairs of anterior molars in the lower jaw accords 

 with the iinusual elongation of the premaxillary or incisor teeth. Were 

 the mandibular plates united at the symphysis (as in all the typical Chi- 

 m8eroids),thepremaxillaries would have overlapped them, aud, having 

 no opposing whetstone to work upon, would have continued growing 

 from the basal pulp-cavity (like the distorted incisor of a Eodent) 

 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 oj)position of the upper and lower teeth, by which a permanent 

 prehensile apparatus is secured for seizing and tearing the prey pre- 

 liminary 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 spe- 

 cimen 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 sem- 

 blance of the wings of a Bat. It appears to be composed of a carti- 

 laginous 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 pro- 

 jecting from the margin of the plate (PI. YIII. o). On either side 

 of the frontal mesial line, and superimposed upon the cartilage, is a 

 cylindrical osselet one inch inlength. These bones have their anterior 

 extremities coincident with the bases of the premaxillary teeth, 

 affording to them support, and perhaps attachment for muscles con- 

 nected with the masticatory function. Dr. Giinther informs me that he 

 has found a pair of nasal cartilages in a similar position in the recent 

 Cliimcera 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 considera- 

 tion, it will, I think, be conceded that this Fish is a novelty in 

 palseichthyology of no ordinary interest. The form of the head, 

 extended in the horizontal instead of the vertical plane, suggests the 

 strange appearance of a Zygcana, but covered with hard jDlates like a 

 Sturgeon. The maxillary teeth most resemble those of CaUorhynclius, 



s2 



