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 premaxillse 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 
Chisel-Jaw. figure q£ the cut on p 479) wag discovered not very many years ago in 
the rivers on the West Coast of Africa, and takes its name from the strong dental 
BEAKED SALMON (J Bat. 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 maxillae. 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. 
