548 TEXTBOOK OF ZOOLOGY 



Suborder — Ophidia (Serpentes). The braincase enclosed by descending 

 plates from parietals and f rentals; no external limbs present. This 

 suborder includes all snakes. 



Subclass — Diapsida. Temporal region of the skull with two openings. 



Order — Bhynchocephalia. Amphicoelous vertebrae, premaxillae with a de- 

 curved beak; pineal eye present. 



Suborder — Sphenodontia. Has the characters of the order. Sphenodon, 

 the single living genus of this order is famous as being one of the 

 primitive living reptiles. It is found in New Zealand and on pome 

 smaller islands of that region. 

 Order — Crocodilia. Procoelous vertebrae; premaxillae never decurved; no 

 pineal eye present. Crocodiles and Alligators. 

 Suborder — EusucMa. Has the characteristics of the order. 



The living crocodiles and alligators belong to this suborder. 



Order Testudinata (Chelonia) 



Suborder Pleurodira. — Turtles of this group are found in South 

 America, Africa, and Australia. They are known as "side neck" 

 turtles because they do not retract the head and neck under the 

 carapace but lay it along the periphery of the shell. Some members 

 of the group have a pair of bones, the mesoplastra, in the plastron 

 that is not present in other living turtles, though it was common 

 among forms now known only as fossils. The bones of the pelvic 

 girdle are sutured to the plastron as well as to the sacral vertebrae. 

 This is also a characteristic unique among living forms but more 

 common in extinct species. Hence, it is thought that members of 

 this suborder are more primitive in structure than the members of 

 either of the other two suborders having living representatives. 



Suborder Cryptodira. — There are sixty-one species of turtles in 

 North America north of Mexico or in the oceans that bound the 

 shores of this region. Fifty-seven of this number belong to this 

 suborder. Six families are represented. 



Family Kinosternidae. — This family includes the turtles commonly 

 known as the "mud turtles,"' "stinkpots," or "musk turtles." 

 They are all small, brown or black turtles, sometimes with white 

 or yellow lines on the head and neck. Many turtles are fre- 

 quently mistaken for members of this family that belong to 

 some other family. In California, where no kinosternid turtle is 

 found, a member of the family Emydidae is called the "mud turtle." 

 All kinosternids possess musk glands that open through pores on 



