IV. VERTEBRATA: REPTILIA, RHYNCHOCEPHALIA. 527 



condition of the quadrate, the lack of an os transversum and of any but basi- 

 sphenoid of the sphenoidal bones {Dennochelys has a parasphenoid), and the 

 growth forwards and backwards by which the girdles are brought inside the ribs. 

 The teeth are entirely lost, and, as in birds, the jaws are enclosed in sharp 

 horny beaks, in many cases efficient weapons against larger vertebrates. The 

 cloaca! opening is oval, its major axis corresponcUng to that of the body, and in 

 its anterior end is an unpaired erectile penis used in copulation. Turtles 

 appeared in the Permian. 



Characters of armor and legs serve to contrast sharply the land and sea 

 turtles; the first with well-developed legs, iive-toed in front, four-toed behind, 

 the toes with claws; the carapace arched, into which legs, head, and tail may be 

 retracted. In the sea turtles the feet are flipper-like (fig. 576), claws mostly 

 absent, and the carapace weakly united to or free from the plastron, flat and 

 incapable of covering head or appendages. The fresh-water species are inter- 

 mediate in position. 



Sub Order I. ATHECA. Carapace of numerous mosaic scales not con- 

 nected with ribs and vertebrfe; skin leathery. Dermnchelys* leather-back 

 tortoise, reaches a weight of 1500 pounds. Sub Order II. TRIONYCHIA. 

 Fresh-water forms with poorly ossified carapace, but ribs and vertebras connected 

 with it. Leather turtles (Amyda*) and soft-shelled turtles LAspidonectes*). 



Fig. 576. — Eretmochelys inibricata, tortoise-shell turtle (from Hajek). 



Sub Order III. CRYPTODIRA. Carapace well developed and united with 

 ribs and vertebrae, but the pelvic arch free. Species numerous, including ter- 

 restrial, fresh-water, and marine forms. Chelydrid^, fresh water, tail long. 

 Chelydra serpentina* snapping turtle; Machrochelys lacerlina* alligator turtle. 

 Chelonid.5;, marine, paddle-like feet. Thalassochelys* loggerhead; Chelone 

 mydas* green turtle; Eretmochelys imbricala, whose horny shields furnish 

 'tortoise shell.' Testudinid.5;, terrestrial, including Xerobates,'*- the 'gopher 

 turtle' of the South, the giant Testudo of the Galapagos Islands, and the fossil 

 Colossochclys atlas of India, 18-20 feet long, 8 feet high. Other families contain 

 our mud turtle (Kinosternon*), box turtles (Cistiido'''), and terrapins {Mala- 

 demmys*). Sub Order IV. PLEURODIRA. Pelvis united to carapace and 

 plastron; southern hemisphere. 



Order V. Rhynchocephalia. 



These resemble the lizards not only in body form (four five-toed feet) and 

 in scaly skin, but in lack of hard palate, presence of epipterygoid, transverse 

 cloacal opening, and heart, lungs, and brain. On the other hand, they recall 

 crocodiles in having two postorbital arches and immovable quadrate. The 

 large abdominal sternum and abdominal ribs are noticeable as well as the 

 uncinace processes of the true ribs. The notochord is but incompletely replaced, 

 the vertebrcB amphicoelous. The group appears in the Permian and is one of the 



