82 SCLERODERMS. 



tated suture. In the upper jaw of many species of Tetrodon, there is 

 a rudimental posterior dental series, consisting of three or four plates 

 which project downwards and backwards from the base of the inter- 

 maxillary bones, and intercept a space in which the apex of the 

 lower jaw is received when the mouth is closed. In Plate 39, fig. 1, 

 is given a figure of the beak-like jaws of the Tetrodon lineatus, showing 

 the median suture, the lines of stratification of the marginal dental 

 plates, and, at (a), the posterior lamelliform teeth above described. The 

 marginal lamelliform teeth are from ten to twelve in number in 

 each half of the mandible ; the innermost are the broadest, and they 

 become narrower as they pass outwards. The intervening portions, 

 or bases of their respective pulps remain longer in the unossified state 

 than in the Diodon. The microscopic structure of the teeth of the 

 Tetrodon closely agrees with that of the dental tubercle of the Diodon. 



SCLERODERMS. 



31. The teeth in the file-fishes (BalistesJ are limited to the inter- 

 maxillary, premandibular and pharyngeal bones. 



In the Batistes forcipatus, PI. 40, the teeth of the upper jaw are 

 fourteen in number, and are arranged in two rows, seven in each inter- 

 maxillary 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, sub trihedral, hollow at the base, 

 which is obliquely truncated, and rounded and obtuse at the apex. 

 The mesial pair is slightly curved, and is the largest ; the rest de- 

 crease in size to the outermost. The external facet of each tooth is 

 covered with a smooth, dense, enamel-like substance, which, towards 

 the apices of the teeth, presents a yellow colour, and calls to mind the 

 peculiar colour of the enamel in some of the Rodentia. These outer 

 maxillary teeth are arranged in close contact with one another 

 (PI. 40, figs. 1 and 7). The form of the alveolus in which the base is 

 fixed, is peculiar in the dental system, resembling rather the surface 

 of attachment for the claw in the ungueal phalanges of the feline 

 quadrupeds. A conical process of the bone rises from the middle of 

 the alveolar depression, and is adapted to the cavity in the base of the 



