56 FISHES OF PENNSYLVANIA. 


cording to Mr. Hessel, yields from four hundred thousand to five hun- 
dred thousand eggs; the scale carp contains rather more than the other 
varieties. During the spawning the fish frequently rise to the surface, 
the female accompanied by two or three males. The female drops the 
eggs at intervals during a period of some days or weeks in shallow 
water on aquatic plants. The eggs adhere in lumps to plants, twigs 
and stones. The hatching period varies from twelve to sixteen days. 
Size.-—According to’ Hessel the average weight of a carp at three 
years is from three to three and one-fourth pounds; with abundance of 
food it will increase more rapidly in weight. The carp continues tc add 
to its circumference until its thirty-fifth year, and in the southern parts 
of Europe Mr. Hessel has seen individuals weighing forty pounds and 
measuring three and one-half feet in length and two and three-fourths 
feet in circumference. A carp weighing sixty-seven pounds and with 
scales two and one-half inches in diameter was killed in the Danube in 
1853. Thereis a record of a giant specimen of ninety pounds from lake 
Zug in Switzerland. Examples weighing twenty-four pounds have 
been caught recently in the Potomac river at Washington, D. C. 
Food.—The carp lives principally on vegetable food, preferably the 
seeds of water plants, such as the water lilies, wild rice and water oats. 
Tt will eat lettuce, cabbage, soaked barley, wheat, rice, corn, Insects and 
their larvee, worms and meats of various kinds. It can readily be caught 
with dough, grains of barley or wheat, worms, maggots, wasp larve and 
sometimes with pieces of beef or fish. 
ORDER ISOSPONDYLI. 
Famity HIODONTIDA.. (Tue Moon-ryss). 
Genus HIODON Le Svevr. 
In the moon-eyes the body is oblong, compressed, covered with cycloid silvery 
scales of moderate size. Head short, naked, with obtuse snout and no barbels. The 
mouth is terminal, of moderate size; jaws subequal. The margin of the upper jaw is 
formed by the non-protractile intermaxillaries and the slender maxiliaries, which 
are articulated to the end of the intermaxillaries. The opercular apparatus is com- 
plete. Intermaxillary and mandible with small cardiform teeth, wide set. Feeble 
teeth on the maxillaries. A row of marginal teeth on the tongue; those in front 
very strong canines. A band of short close-set teeth on middle of tongue. Vomer- 
ine teeth small, close set, in along double series. Teeth on the palatine, sphenoid 
and pterygoid bones. The lower jaw is received within the upper, so that the man- 
dibulary teeth are opposite to those on the palatine bone. The very large eye has a 
little-developed adipose eyelid. Nostrils large, close together, with a flap between 
them. Gill membranes deeply cleft, free from isthmus, their base covered by a fold 
of skin. Branchiostegals eight to ten. No pseudobranchie. Gill rakers short, thick 
