THE PHYLUM CHORDATA 7 



Class 3. Amphibia, amphibians, lowest four-legged vertebrates, skins naked and slimy, 

 or with bony plates (extinct), living in or near water. 

 Subclass i. Stegocephala, extinct amphibia, with tails, and covered with an armor 



of bony plates. 



Subclass 2. Lissamphibia, present-day amphibia, with naked slimy skins (a few with 

 minute, concealed scales). 



Order i. Urodela, with tails; the salamanders and newts, Necturus, Amblystoma, 

 Cryptobranchus, etc. 



Order 2. Anura, tailless; frogs, toads. 

 Class 4. Reptilia, reptiles, air-breathing vertebrates covered with horny scales. 



Order i. Cotylosauria. Most primitive group of extinct reptiles, resembling 

 Stegocephala in skeletal characters. Seymouria. 



Order 2. Chelonia, the turtles, body inclosed in a hard case. 



Order 3. Rhyncocephalia, including but one animal, the Sphenodon (Hatteria) 

 or tuatara of New Zealand, a lizard-like animal with primitive skeletal char- 

 acters. 



Order 4. Squamata, usually of small or moderate size and covered with horny 

 scales. 



Suborder i. Lacertilia, the lizards, nearly always with limbs, eyelids 



movable. 



Suborder 2. Ophidia, the snakes, devoid of limbs, eyelids immovable. 

 Order 5. Crocodilia, the crocodiles, alligators, gavials, and caimans, large 

 reptiles with both horny scales and bony plates in the skin. 



Class 5. Aves, birds, vertebrates with feathers. 



Class 6. Mammalia, mammals, vertebrates with hair and milk glands. 

 Subclass i. Prototheria, mammals laying eggs. 



Order i. Monotremata, the monotremes, or egg-laying mammals, including only 

 the duckbill (Ornithorhynchus) and the spiny anteaters (Echidna and Pro- 

 echidna} of the Australian region. 



Subclass 2. Eutheria, mammals bearing the young alive. 

 Division i. Didelphia or Metatheria. 



Order i. Marsupialia, the marsupials, mammals bearing the young in a very 

 immature state, and carrying them in a pouch formed by a fold of skin on the 

 abdomen, placenta absent or primitive; kangaroos, opossums, etc. 



Division 2. Monodelphia or Placentalia, the placental mammals, without a 



pouch, young nourished in the uterus by a placenta, which is produced 



by a fusion between certain parts of the embryo and certain parts of the 



maternal uterus. This division includes sixteen orders which are described 



in detail in N, pages 346-404. In this manual, we meet with three orders: 



Order Carniwra, the carnivorous mammals, with claws and sharp, cutting teeth; 



the bears, raccoons, minks, martens, weasels, otters, dogs, foxes, wolves, 



cats, lions, tigers, hyaenas, seals, walruses. 



Order Rodentia, the rodents, with chisel-like front teeth, and back teeth with 

 flat, grinding surfaces; the hares, rabbits, squirrels, rats, mice, porcupines, 

 guinea pigs. 

 Order Edentata, teeth lacking or degenerate; the ant bears, sloths, and armadillos. 



