THE GROUPS OF ANIMALS 279 



Class 11. Elasmobranchii. Fishlike vertebrates without air bladder, with jaws, 

 and with a cartilaginous skeleton and placoid scales. Sharks, rays, and skates. 

 (Figs. 251, 252.) 



Subclass I. Selachii 



Order 1. Squali Order 2. Raji 



Subclass II. Holocephali 



Class III. Pisces. Aquatic, cold-blooded vertebrates breathing by means of gills, 

 with air bladder, a two-chambered heart, and usualjy a dermal exoskeleton of scales. 

 Fishes. (Figs. 159, 253.) 



Subclass I. Teleostomi. Fishes with a skeleton consisting wholly or par- 

 tially of bone, breathing by means of gills. True fishes. 



Order 1. Crossopterygii Order 3. Holostei 



Order 2. Chondrostei Order 4. Teleostei 



Subclass II. Dipnoi. Fishes with a skeleton of cartilage and bone, and air 

 bladder functioning as a lung. Lungfishes. 



Class IV. Amphibia. Cold-blooded vertebrates breathing by means of gills in 

 some stage, skin usually not covered with scales, heart of three chambers. Sala- 

 manders, toads, and frogs. (Figs. 93, 151, 157, 158, 163, 187, 254, 255.) 



Order 1. Caudata Order 3. Apoda 



Order 2. Salientia 



Class V. Reptilia. Cold-blooded vertebrates usually covered with scales, breath- 

 ing throughout life by means of lungs. Lizards, snakes, crocodilians, turtles. (Figs. 

 156, 256, 257, 279, 281.) 



Order 1. Testudinata Order 3. Crocodilini 



Order 2. Rhynchocephalia Order 4. Squamata 



Class VI. Aves. Warm-blooded vertebrates with the body covered with 

 feathers, with the forelimbs usually modified as wings, and a heart of four chambers. 

 Birds. (Figs. 161, 201.) 



Archaeornithes 

 Neornithes 

 Struthioniformes. Ostriches. 

 Rheiformes. Rheas. 

 Casuariiformes. Cassowaries, emus. 

 Apterygiformes. Kiwis. 

 Tinamiformes. Tinamous. 

 Sphenisciformes. Penguins. 

 Gaviiformes. Loons. 

 Colymbiformes. Grebes. 

 Procellariiformes. Albatrosses, petrels. 

 Pelecaniformes. Pelicans, frigate birds. 

 Ciconiiformes. Herons, storks. 

 Anseriformes. Ducks, geese, swans. 

 Falconiformes. Vultures, hawks, falcons. 

 Galliformes. Pheasants, grouse, turkeys. 

 Gruiformes. Cranes, rails. 

 Charadriiformes. Shore birds, gulls, auks. 



