MOON-EYE AND CHISEL-JAW. 



479 



the pharyngeal bones numerically the same as in the southern pikelets, on which 

 account Professor Cope regards it as the type of a distinct family. Differing from 

 the other two genera in the comparatively small size of the cleft of the mouth, and 

 also in the approximate equality of the length of the jaws, this fish has no barbels, 

 and only a single series of teeth in the jaws, teeth being also present on the 

 pterygoid and hyoid bones, but wanting on the vomer and palatines. A further 

 peculiarity is to be found in the presence of a peculiar spiral organ on the fourth 

 gill-arch ; and the air-bladder differs from that of the other members of the family 

 in its cellular structure, while the stomach comprises a membranous and a muscular 

 portion. The fish in question is found alike in the upper Nile and in the rivers of 

 Western Africa. It grows to about 2 feet in length. 



MOON-EYE AND CHISEL-JAW, Families HYODONTID^J and PANTODONTID^. 



Each of the two fishes figured in the annexed illustration is the only represent- 

 ative not only of a genus, but likewise of a separate family ; these families agreeing 



CHISEL-JAW AND MOON-EYE (J nat. size). 



with all the remaining ones of the present section in having the pterotic bone 

 normal, the base of the skull double, and four upper pharyngeal bones, all of which 

 are distinct, and the third the largest and directed forwards. In the first family 

 the parietal bones are united, and there are two true tail-vertebrae in front of the 

 complex bone supporting the rays of the caudal fin. 



