CHIEF DIVISIONS OF THE ANIMAL KINGDOM. 87 



Heart usually of two chambers, rarely of three. Blood cold. Limbs, 

 when present, converted into fins. 



Order 1. Pharyngobranchii. Ex. Lancelet (Amphioxus). 



Order 2. Marsipobranchii. Ex. Lamprey (Petromyzon), Hag-fish 



(Myxine). 



OrderS. Teleostei (Bony Fishes). Ex. Eels (Muramidee), Her- 



rings (ClupeidaB), Salmon and Trout (Salmonidae), 



Cod and Haddock (Gadidse), Flat-fishes (Pleuronec- 



tidse), Perch (Percidse), Mackerel (Scomberidse). 



Order 4. Ganoidei. Ex. Bony Pike (Lepidosteus), Paddle-fish 



(Spatularia), Sturgeon (Sturio). 



Order 5. Elasmobranchii. Ex. Sharks (Carcharidse), Dog-fishes 

 (Scylliadse), Saw-fishes (Pristis), Kays and Skates 

 (Raiidse). 



Order 6. Dipnoi. Ex. Mud-fish (Lepidosiren), Ceratodus. 

 CLASS II. AMPHIBIA (Amphibians). Breathing-organs in the young 

 in the form of gills alone, afterwards lungs, either alone or associated with 

 gills. Skull joined to the backbone by two articulating surfaces (" cori- 

 clyles"). Limbs never converted into fins. Heart in the young of two 

 chambers only, in the adult of three chambers. Blood cold. 

 Order 1. Labyrinthodontia (extinct). 

 Order 2. Ophiomorpha. Ex. Csecilia. 



Order 3. Urodela (Tailed Amphibians). Ex. Water-newts (Tri- 

 ton), Salamanders (Salarnandra), Axolotl (Siredon), 

 Mud-eel (Siren). 

 Order 4. Anoura (Tailless Amphibians). Ex. Frogs (Rana), Tree- 



frogs (Hyla), Toads (Bufo), Surinam toads (Pipa). 

 CLASS III. REPTILIA (Reptiles). Respiratory organs in the form of 

 lungs, never in the form of gills. Heart three-chambered, rarely four- 

 chambered, the pulmonary and systemic circulations always connected 

 together directly, either in the heart itself or in its immediate neighbour- 

 hood. Blood cold. Skull jointed to the backbone by a single articulat- 

 ing surface or " condyle." Each half of the lower jaw composed of seve- 

 ral pieces. Appendages of the skin in the form of scales or plates. 



Order 1. Ohelonia. Ex. Turtles (Cheloniidae), Soft Tortoises 

 (Trionycidse), Terrapins (Emydidse), Land Tortoises 

 (Testudinidse). 



Order 2. Ophidia. Ex. Vipers (Viperidse), Rattlesnakes (Crota- 

 lidae), Sea-snakes (Hydrophidse), Boas and Pythons 



OrderS. Lacertilia. Ex. Lizards (Lacerta), Iguanas (Iguanidae), 

 Monitors (Varanidae), Chameleons (Chamaeleontidse). 

 Order 4. Crocodilia. Ex. Crocodiles, Alligators, Gavials. 

 Order 5. Ichthyopterygia (extinct). Ex. Ichthyosaurus. 

 Order 6. Sauropterygia (extinct). Ex. Plesiosaurus. 

 Order 7. Pterosauria (extinct). Ex. Pterodactylus, Pteianodon. 

 Order 8. Anomodontia (extinct). Ex. Dicynodon. 



