KEY TO CLASSES AND ORDERS OF ANIMALS 49 



Subclass TELEOSTOMI 



1(4) Tail heterocercal; fins without spines; rudimentary 

 spiral valve in intestine; heart with a conus arteriosus. 



2 



2(3) Skeleton chiefly cartilaginous. (Forbes and Richard- 

 son, 21.) Order Chondrostei 



3(2) Skeleton bony. (Forbes and Richardson, 30 and 37.) 



Order Holostei 



4(1) Tail homocercal; fins frequently with spines; spiral 

 valve and conus arteriosus lacking. (Forbes and 

 Richardson, i.) Order Teleostei 



Class AMPHIBIA 



1(2) Adults with tails; body elongated; legs of approxi- 

 mately equal size; salamanders, newts, and mud- 

 puppies. (Jordan, 186.) Order Urodela 



2(1) Adults lacking tails; body short and stout; hind legs 

 much longer than fore legs. (Dickerson, 43.) 



Order Anura (Salentia) 



Class R E P T I L I A 



1(2, 3) Short compact body inclosed in a hard case or shell 

 from which only head, tail and legs protrude; cloacal 

 opening oval; turtles and tortoises. (Ditmars, 3.) 



Order Chelonia 



2(1, 3) Body elongated; legs present or absent; cloacal 

 opening transverse; body covered with scales some- 

 what as in fishes; snakes and lizards. (Ditmars, 95 

 and 207.) Order Squamata 



3(1, 2) Lizard-like in shape but may attain a size of ten feet 

 or more; cloacal opening, oval; scales and bony plates 

 in the skin; jaws extend to form a long snout; tail 

 flattened laterally. (Ditmars, 83.) 



Order Crocodilia 



