480 



TUBE-BLADDERED GROUP, 



Moon-Eye. 



Externally, the moon-eye (Hyodon tergisus), as the single 

 representative of the first of the two families is popularly termed, has 

 the body covered with cycloid scales, the head naked, and no barbels. The margin 

 of the upper jaw is formed by the premaxillae in front and the maxillae at the sides, 

 the latter bones being articulated to the former at the point of junction ; and all 

 the elements of the gill-cover are present. There is no fatty fin, and the short 

 dorsal is placed in the caudal region, above the fore-part of the longer anal ; the 

 caudal fin being forked. The gill-openings are wide ; the stomach is horseshoe- 

 shaped, the intestine short, and the air-bladder simple ; false gills being absent. 

 In form the body is oblong and compressed, with a part of the lower surface form- 

 ing a sharp edge ; and the cleft of the mouth is somewhat oblique ; all the bones of the 

 palate bearing small teeth, and the edges of the tongue carrying a larger series. 

 Before their exclusion, the eggs fall into the cavity of the abdomen. The moon- 

 eye, shown in the lower figure of the cut on p. 479, grows to a length of from 

 1 foot to 18 inches, and is confined to the fresh waters of North America, where 

 it is abundant in the lakes and rivers of the western side of the continent. 



The small fish (Pantodon buchholzi) represented in the upper 

 figure of the cut on p. 479, was discovered not very many years ago in 

 the rivers on the West Coast of Africa, and takes its name from the strong dental 



Chisel-Jaw. 



beaked salmon (J nat. size). 



armature of the jaws. Remarkably like a cyprinodont in external appearance, 

 this fish has the body covered with relatively large scales, and the sides of the head 

 with bony plates ; the margin of the upper jaw being formed in front by the united 

 premaxillse, and at the sides by the maxillse. The short dorsal fin is situated still 

 further back than in the last genus, its front margin being considerably behind 

 that of the rather longer anal ; both the pectoral and pelvic fins are very tall, the 

 rays of the latter forming isolated filaments, and the caudal is long . and pointed, 

 with some of its rays projecting. The muzzle is blunt, and the cleft of the mouth 

 directed upwards. In the gill-cover there is only an opercular and a preopercular 

 bone, the gill-openings are wide, and the branchiostegal rays are numerous. 

 False gills are absent ; the air-bladder is simple ; and the ovaries of the female, 

 and the corresponding organs of the opposite sex, are furnished with a duct. 



