58 



HIGH SCHOOL ZOOLOGY. 



circulates ; its meaning will afterwards be explained. This 

 family is characteristically a fresh- water one, the section of the 

 Catosomidae being nearly confined to North America, and in- 

 cluding our suckers, lake-mullet (Fig. 23), carp and carp-suckers, 

 while the rest of the Cyprinoids are abundantly represented in 

 the Old "World as well as the New. The suckers and their allies 

 attain a large size, but the rest of the group are small and very 

 similar in form and colour, so that they are difficult to diagnose, 

 and much remains to be found out as to their distribution in 

 Canada. Two further peculiarities of the family may be re- 

 ferred io, the bright colouring of the males at breeding time in 

 the spring, and the division of the air-bladder into two or three 

 compartments by ti-ansverse constrictions. 



Fig. 23.— The Red Horse. Moxostoma macrolepidotum. |. 

 (U. S. Fish Commission.) 



10. The Siluroids and Cyprinoids, like several other fomi- 

 lies of Teleostei, have an open duct between the air-blaclder 

 and the oesophagus ; all the families which possess this are 

 known as the Physotomous Teleosts, while those in which the 

 air-duct is absent are known as the Physoclystous Teleosts. We 

 shall find some familiar forms among the remaining Physostomi, 

 which haA^e the anterior vertebrfe separate from each other and 

 unconnected with the air-bladder. Foremost in importance, 

 from an economical point of view, is the family of the Salmon- 

 idse, which contains so many valuable food-fishes. Chief among 

 these is the Atlantic salmon, (^Salmo solar, Linn.) (Fig. 24) 



