Phylogeny 



The Engystomatidae are tropical in their distribution. The 

 only North American species found outside of southern Texas 

 is Engysioma carolinense. This is found in a belt across the con- 

 tinent from Florida to Texas, inclusive, and as far to the north as 

 Virginia (Cape Charles), southern Illinois, and Missouri. (Refer 

 to p. 1 66.) 



Family VII . Ranidce 



The Family of the Ranidas is the most specialized of the 

 Salientia; it is also one of the most unified families in its structural 

 characteristics. The shoulder-girdle is not only always firmis- 

 ternal in type, but also usually agrees with the type for the fam- 

 ily in its details (such as the presence of the precoracoids and a 

 well-developed omosternum and sternum furnished with a bony 

 style). The cranium also constantly shows the same character- 

 istics (such as the absence of a frontoparietal fontanelle). 



The family contains a large number of genera, and it is very 

 widely distributed. Australia, New Zealand, and southern South 

 America are the only parts of the world not possessing represent- 

 atives of the true frogs. Some two hundred species (by far the 

 largest number) are found in the tropical portion of the Eastern 

 Hemisphere. North America has only one genus, Rana; there 

 are seventeen known species, and one form of the rank of a sub- 

 species {Rana c. laiiremis). They are most numerous in the 

 eastern part of the continent, though several species are found 

 west of the Sierra Nevada Mountains. See p. 171. 



V. Phylogeny 



It is not until recent years that the Batrachians have been 

 recognized as a distinct Class, intermediate in position between 

 the Fishes and the Reptiles. This is partly because of the rela- 

 tively high specialization of some of the living batrachian species, 

 a specialization that removes them from the direct line of evolution 

 and makes necessary a large amount of comparative morphologi- 

 cal and embryological investigation before their true relationship 

 can be discovered. In France and Germany, in England and 

 lastly in America, this work has been going on since the time 

 of Linnaus in the eighteenth century. Linnaeus classified Batra- 

 chians, some of the Fishes, and Reptiles together, calling them 

 Amphibia. Since then Batrachians have been classified with 



II 



