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CHAPTER LIV. 



CLASS REPTILIA — continued. 



Orders Ichthyopterygia, Proterosauria, Rhynchocephalia, 

 and squamata. 



Streptostylic Branch. — According to the arrangement pro- 

 posed by Dr Baur, 'this branch is taken to include the four orders 

 mentioned in the heading of this chapter. These orders present a 

 remarkable instance of the divergent views obtaining among different 

 writers as to the classification of Reptiles. Thus Professor Cope 

 has proposed to place the Ichthyopterygia in a group by themselves, 

 which he regards as of equal value to another containing all the 

 other orders ; while Professor Seeley at one time regarded this order 

 as a division of the Dinosauria, although its relationship to the 

 Squamata had been long before pointed out by Sir R. Owen. Pro- 

 fessor Seeley has also proposed to separate the Squamata from all 

 other Reptiles under the name of Coenosauria, and to include the 

 Rhynchocephalia in a second division as Palaeosauria. Professor 

 Cope, while not going so far as this, places the Rhynchocephalia in 

 the Synaptosaurian branch ; while Professor Huxley would include 

 both that group and the Proterosauria in the Squamata (Lacertilia), 

 from which the Ophidia are excluded. Dr Baur, again, merges the 

 Proterosauria in the Rhynchocephalia, and regards the latter as a 

 distinct order allied to the Squamata. This middle course is fol- 

 lowed in the present work, although the Proterosauria, in accordance 

 with the views of Professor Seeley, are provisionally allowed to rank 

 as an order. 



The present branch may be collectively characterised as follows : 

 The dentition is very generally either acrodont or pleurodont, with 

 the teeth of the adult anchylosed to the jaws ; but the teeth may 

 be implanted in a groove, and remain free. In addition to their 

 presence in the jaws, teeth may also be developed on the palatine 

 and pterygoid, and very rarely on the vomer. . There is very fre- 



