76 



Order VI. PLECTOGNATHI. 



Family Balistida. File-fish. 



326. The skeleton of a File-fish (Balistes). 



The anterior interneural spine is bent abruptly forwards, and its summit is much developed 

 and articulated to the back part of the occipital spine : it is excavated at its upper and poste- 

 rior surface, and in this cavity two dermoneural spines lie concealed when recumbent. These 

 spines are articulated to the fore part of the interneural expanded plate by the peculiar linked 

 form of joint common to such species : when both are erected, the fore part of the base of the 

 smaller anterior spine fits into the back part of the base of the large one, and fixes it in the 

 erect position like the lock of a gun at full cock. The small spine requires to be moved by 

 its muscles before the larger one can be bent back. 



The orifices for the spinal nerves are pierced through the middle of the base of the neur- 

 apophyses. The pelvic bones and the epicoracoids are both remarkably developed. 



The number of abdominal vertebra is 6, that of the caudal vertebrae, 1 1 : total, 1 7. 



Purchased. 



327. The skull of a File-fish (Balistes forcipatus) with the skin left on the right side, 



showing the rough ganoid surface of the scales. The exposed bones on the 

 opposite side are indicated by the numbers, according to those in Table I. 



The pelvic bones are of remarkable length ; they are attached to the symphysis of the 

 coracoids. The mesotympanic is unusually long and slender, reaching almost to the joint for 

 the lower jaw : it is continuous in the recent fish with the cartilage which enters the cavity 

 of that jaw. The palatine bone is small and hammer-shaped ; one end of its expanded head 

 articulates with the prefrontal, the opposite end with the maxillary : the coalescence of this 

 bone with the premaxillary and of the articular with the dentary piece in the lower jaw are 

 the characters signified by the name ' Plectognathi,' which Cuvier has given to the family of 

 fishes to which the genus Balistes belongs. The extraordinary downward development of 

 the vomer and the large basicranial canal are worthy of notice in this specimen. 



Mas. Brit. 



328. The premaxillary, premandibular, and one of the maxillary bones of the Balixh-x 

 forcipatus. 



In this species the teeth of the upper jaw are 1 4 in number, and are arranged in two rows, 

 seven in each intermaxillary bone, four in the front row and three behind. In the lower jaw 

 there are eight teeth corresponding with the front row above. The anterior or external teeth 

 of the upper resemble those of the lower jaw ; they are strong, conical, subtrihedral, hollow 



