FAMILY CYPRINIDAE 139 



teeth, the inner or main row 4 or 5. The tooth, or dental, formula 

 when given for a species means the number of teeth in each of the 

 four rows from left to right. The formula 2, 5 — 4, 1 means that the left 

 side has 2 outer and 5 inner teeth and the right side has 1 outer and 4 

 inner teeth. 



In order to be observed the teeth must be carefully dissected out. The 

 dissection is done by turning back the opercle and exposing the last 

 gill-arch, which bears the teeth. This arch lies against and inside the 

 shoulder girdle, which supports the pectoral fins. The last arch on each 

 side must be carefully separated from the girdle by cutting, and then 

 is removed by cutting at each end. The tissue must be dissected away 

 from the teeth with needles and care taken not to injure the teeth, 

 which are easily broken. 



The various species of the family also show considerable difference 

 in the selection of food from the general supply available to them. The 

 minnows of Minnesota and neighboring states are mainly carnivorous, 

 though they seldom eat fishes or the other larger aquatic animals. A few 

 species eat largely of vegetation, and a few others feed almost wholly 

 on the highly organic mud of the bottoms of ponds and streams, but the 

 principal diet of most minnows consists of insects and Crustacea 

 (Entomostraca) . 



Forbes and Richardson in 1908 wrote: "In the general scheme of 

 aquatic life, the native members of this family, taken together as a 

 group, play a multiple role. They operate, to some extent, as a check 

 on the increase of the aquatic insects, from which they draw a large part 

 of their food supply; they make indirectly available, as food for their 

 own most destructive enemies, these aquatic insects, many terrestrial 

 insects also, which fall into the water and are greedily devoured by 

 them, and the mere mud and slime and confervoid algae gathered up 

 from the bottom of the waters they inhabit; and they rival the young 

 to a great degree, of all larger fishes, their own worst enemies included 

 by living continuously, to a great degree on the Entomostraca and insect 

 life which these fishes must have, at one period of their lives, in order 

 to get their growth. They also offer a considerable means of subsistence 

 to certain aquatic birds . . . and, through their contributions to the 

 support of the best food fishes, they form an important link in the chain 

 of agencies by which our waters are made productive in the interest 

 of man. . . . 



"From the standpoint of the predaceous species, minnows are young 

 fishes which never grow up, and thus keep the supply of edible fishes of 

 a size to make them available to the smaller carnivorous kinds when the 

 young of the larger species have grown too large to be captured or 

 eaten. . . . Moreover, by their great numbers, by their various adapta- 

 tions and correspondingly general ecological distribution, and by their 

 permanently small size, the minnows must distract in great measure 



