258 Field Museum of Natural History — Zoology, Vol. VII. 



teeth, as the genera are based largely on dental characters. The 

 teeth are confined to the pharyngeal bones which are just back of the 

 gill openings on either side of the oesophagus. In American species 

 the teeth on each pharyngeal bone are in one large row of 4 or 5, in 

 front of which is usually a smaller row of one or two teeth. The 

 pharyngeal bones must be removed with great care to avoid breaking 

 the teeth from them. It is best to clean the teeth by tearing away 

 the flesh with a needle or other sharp-pointed instrument, after which 

 they are easily examined with a hand lens. The herbivorous species 

 have teeth usually not hooked and with a flat or concave surface. In 

 the carnivorous species they usually have a sharp cutting or a serrated 

 edge and hooked tips. Their number is indicated by a dental formula. 

 Thus "teeth 4-4," indicates that only the principal row on each side 

 is present. "Teeth 2. 4-5, 2," indicates the principal row on one side 

 contains four teeth, the other five, while the lesser row on each side 

 contains two each, and so on. 



During the breeding season the males are more or less covered with 

 tubercles, outgrowths of the epidermis. Usually these are confined 

 to the head, but often are found over the entire body. The lower 

 parts of the body and the fins are often highly colored ; the prevailing 

 color being red, although in some genera it is satin white, yellow, or 

 black. In some cases the males are deeper than the females. Young 

 examples are always difficult to identify; these are usually more 

 slender and have a larger eye than the adults. Often the young have 

 a lateral band and a dark caudal spot which the adults do not possess. 

 In the following descriptions the rudimentary rays of the dorsal and 

 anal fins are not counted. Besides the native species here mentioned, 

 three species from Europe and Asia have been introduced into some of 

 the streams and lakes of the United States and Mexico, where they 

 have become quite abundant. They are easily distinguished from 

 the native fresh-water fishes by the long dorsal fin which is preceded 

 by a serrated spine. 



a. Anterior dorsal rays not forming a stifif serrated spine; dorsal 

 fin of less than 10 rays. 



b. Alimentary canal more than twice the length of the body; peri- 

 toneum usually black, or dark gray. 



c. Air bladder surrounded by convolutions of the intestine; about 

 50 scales in the lateral series, teeth 4-4 or i, 4-4, o. 



Campostoma , 260 

 cc. Air bladder not surrounded by convolutions of the intestine. 



d. Scales very small 65 to 90 in the lateral series; teeth 5-5 or 4-5. 



Chrosomus, 260 



