88 Dynamic Theory. 



They are further related to the birds in having an additional clavicle, 

 something like the furcula or forked wish-bone of the birds, and also 

 webbed feet ; beside which the males have a spur on each hind leg, and 

 the muzzle of the Ornithorhyncus is flat and projecting like the bill of 

 the duck. Nevertheless they are mammals possessing milk glands 

 without nipples, the young drawing their nourishment through pores or 

 ducts in the skin. The Monotremes have the pouch bones, or marsupial 

 bones, but they have no pouch. The young are probably left in their 

 burrows instead of being carried about. They have no external ear. 

 The Echidna has no teeth but some horny spines instead. The Platypus 

 has in each jaw four back teeth, set in the flesh without roots. 



The animal is covered with fur and is aquatic in its habits. 



The Jurassic Period rather emphasizes what has been said of the 

 Triassic. 



The Cycad and its conifer congeners formed the heaviest part of the 

 vegetation. Le Conte says this might be called the Age of Gymno- 

 sperms,* as the Carboniferous Age is called that of Acrogens. As to 

 animals, the Ammonite family becomes very abundant. They vary in 

 diameter from half an inch to three feet. The genus Ammonite musters 

 about 500 species during the Mesozoic Age. Large Belemnites, the 

 ancestors of the squid, are found. They flourish during this and the 

 Cretaceous period and then become extinct. The Placoidean family, 

 the sharks, now take on their modern teeth and become JSqualodont, or 

 shark-toothed (Squalus, a shark). 



The Jurassic is remarkable for its development of odd and anoma- 

 lous reptile forms, some of them huge and terrible. These are divided 

 into three sections, the marine Saurians ( Enaliosaurs ), the land Sauri- 

 ans (Dinosaurs) and the flying Saurians (Pterosaurs). 



In the first section is the Ichthyosaurus (fish Saurian). He was 

 something like an alligator in appearance from 10 to 40 feet long, 4 

 paddles something like those of a whale, head large, mouth long, set 

 with sharp, conical, striated teeth, sometimes 200 in number, tail long 

 and expanded vertically into a fin, eyes immense 12 to 15 inches in 

 diameter. The vertebral joints were bi-concave like the fishes, instead 

 of having the ball and socket attachment as with the living reptiles. He 

 was carnivorous. Over 30 species of this chap have been found. The 

 Plesiosaurus was another. His neck was long and tail short. His pad- 

 dles were long. His total length was from 25 to 30 feet. 



Pliosaur was another marine Saurian 30 to 40 feet long, something 

 like the other, but more on the lizzard order. The land section Dino- 

 saur contained the Megalosaurus, -a carnivorous Saurian 30 feet long. 



*This word means having naked seeds ; and they comprise the Pine, Hemlock, Spruce, 

 Cypress, Yew, Juniper, Arbor Vitae, &c. 



