346 PALiEOZOIC TIME — CARBONIFEROUS AGE. 



before its final burial by the deposits that were increasing around 

 it ; and along with mineral charcoal derived from the wood, and the 

 bones of the Eeptiles, there were also more than fifty shells of the 

 land-snail Pupa velusta, and the Myriapod above alluded to, besides 



Saurians. — The Saurians vary in length from a few inches to fifty or more 

 feet. In some the teeth are set in sockets, — whence they are called Thecodont 

 Saurians (from On^, a case, and odovg, tooth). In others (Pleurodonts) the teeth are 

 implanted in a groove, the outer horder of which projects more than the inner; in 

 others (Acrodonts) they are soldered firmly to the salient part of the jaw-bone. 



The prominent tribes are as follow, beginning with the highest in rank : — 



1. Dinosaurs (dsivog, terrible, and aavpos, a lizard). — Reptiles of great size, 

 all now extinct, having many mammalian characteristics: (1) the long bones 

 have a medullary cavity; (2) the feet are short, and, with the exception of the 

 ungual phalanges, like those of pachyderms ; (3) the sacrum consists of at 

 least Jive united vertebrae ; (4) the lower jaw in some species has lateral motion for 

 trituration. (Pictet.) Include the huge Megalosaur, Hylseosaur, Iguanodon, etc. 

 In the sacrum made up of five united vertebrae, and some other characters, these 

 species approach the mammals, and show their superiority to all other Reptiles. 



2. Crocodilians, or Cuirassed Saurians. — Body having (1) a cuirass made of 

 bony plates; (2) large, conical teeth in sockets in a single row; (3) one jugale; 

 two premaxillary bones; (4) sacrum formed in general of two vertebrae; (5) 

 heart with four cavities ; external nostrils at the extremity of the snout. The 

 modern species have concavo-convex vertebrae, — that is, the anterior face is con- 

 cave and the posterior convex ; in others, as the extinct Cetiosaur and Steneo- 

 saur, they are convexo-concave ; and in a third group, including the extinct 

 Teleosaur, Macrospondylus, etc., they are doubly concave. 



3. Lacertians, or Scaly Saurians. — Body having (1) corneous scales; (2) the 

 teeth rarely in sockets; (3) no jugale; one ventricle, one premaxillary bone ; 

 (4) sacrum consisting of two vertebrae at the most. The Lizards, Iguanas, and 

 Monitors are the types of the tribe. 



A few extinct species characterized by small scales are Thecodonts, like the 

 Crocodiles, so that they- stand apart from other Lacertians, and are intermediate 

 between them and Crocodilians. Such are the Thecodontosaur, Palseosaur, and 

 Proterosaur (fig. 617 A), — among the earliest of true Reptiles, and the pre- 

 cursors of the Crocodiles and Dinosaurs. 



The Mosasaur (fig. 792), on the contrary, although of large size (twenty-five 

 feet long), had the teeth inserted in a groove, as in the modern Lacertians. The 

 same was the case with the Geosaur ; and both are related to the Monitor of the 

 Nile ( Varanus Niloticus). 



Besides these tribes, there are two extinct groups : — 



4. En alios AURS (from tvaKioq, marine, etc.), or Swimming Saurians. — (1) Fur- 

 nished with paddles for swimming; (2) having the vertebrae biconcave, — another 

 fish-like characteristic; (3) teeth large, and set in a groove. Ichthyosaur and 

 Plesiosaur are the most common genera. (See figs. 708-713, 715.) 



5/ Pterosaurs (from nrepov, a wing, etc.), or Flying Saurians. — The most common 

 genus is Pterodactyl (fig. 739). By the excessive elongation of the little finger of 



