542 



HISTORY OF THE HUMAN BODY 



Order 4. Stegocephali. 



Sub-Order I. Branchiosauria (Branchiosaurus) . 



Sub-Order 2. Aistopoda (snake-like forms, with- 

 out limbs). 



Sub- Order 3. Microsauria (small forms, in shape 

 like salamanders). 



Sub-Order 4. Labyrinthodontia (Archcegosaurus, 

 Mastodonsaurus) . 



[Of the four Orders of Amphibia, one is entirely extinct 

 and the other three essentially modern, and with few 

 traces of older representatives. With regard to the ex- 

 tinct group, that of Stegocephali, it could be placed in 

 the list either at the first or the last, since it shows strong 

 affinities to both ganoids and reptiles and thus lies inter- 

 mediate between the two. The modern Orders seem to 

 have arisen directly from the Stegocephali, the Urodela 

 being the least altered and hence the most important 

 morphologically. This complex relationship between the 

 groups mentioned, the Ganoidei, Stegocephali, Urodela, 

 Reptilia, etc., cannot thus be represented in linear lines 

 but may be partly expressed in the form of a tree, as in 

 the diagram given in Chapter II. (p. 28). The three modern 

 Orders of Urodela, Gymnophiona, and Anura, are quite 

 distinct from one another, and, the first and third espe- 

 cially, are well represented in the living fauna.] 



Super-Class II. Sauropsida. 

 Class III. Reptilia. 



Order i. Theromorpha. 



Sub-Order i. Pariasauria (Pariasaurus). 

 Sub-Order 2. Theriodontia (Cynognathus; Trity- 



lodon). 

 Sub-Order 3. Dicynodontia (Dicynodon; Gordo- 



nia). 

 Order 2. Sauropterygia (Pleisiosaurus; Cryptocli- 



dus). 

 Order 3. Chelonia. 



Sub-Order i. Cryptodira (the majority of living 



turtles). 



Sub-Order 2. Pleurodira (Miolania; Chelys). 

 Sub-Order 3. Trionychia (soft-shelled turtles). 

 Order 4. Ichthyopterygia (Ichthyosaurus). 



