HIGH SCHOOL ZOOLOGY. 



55 



Fig. 20. — Stone Cat. Nnturus gyriniis. 

 (After Jordan). 



Sheat-fish (Silurns glanis) of the Danube. By adding the 

 patronymic ending " idae" to the stem of the generic name of this 

 fish, the family name Siluridae is formed wliich thus inchides all 

 the genera of the group. Family names are generally formed 

 in this way from some typical or well known genus, and if it 

 is considered desirable to arrange the family into sub-families 

 the termination "ina" is generally employed for such smaller 

 groups. But, as in the case of species and genera, zoologists are 

 by no means at one in recognizing the same limits to the classifi- 

 catory sub-divisions employed. Nevertheless the divisions of 

 various rank are always subordinated to each other in a definite 

 way, thus each of the great primary divisions of the Animal 

 Kingdom or Sub-Kingdoms is divided into Classes, each Class 

 into (Sub-Classes and) Orders, each Order into (Sub-Oz'ders and) 

 Families, while each Family (sometimes sub-divided into Sub- 

 Families or Tribes) includes one or more genera according as 

 the species belonging to it are moi-e or less nearly allied to each 

 other. 



8, Thvis the Siluroid family as generally understood is one 

 of the largest of the class Pisces ; it is also a very heterogeneous 

 one, embracing such different forms as our Catfish and the 

 curious mailed Siluroids of the Soutli American Rivei's, so that 

 certain authorities consider it to have the rank of an Order 

 (Nematognathi), and it certainly does contain forms which are 



