1888.] of Reptilian Character in Mammalian Teeth. 141 



incisor cusp of Deuterosaurus, for it is equally developed in successional 

 teeth, which have not come into use. Thus, Amblyrhynchus makes a 

 partial combination of the characters of Ameiva and Teius, and shows 

 what may be termed a sub-mammalian type. 



Fig. 8. 



Anterior aspect. Lateral aspect. External aspect. 



4 



Teeth of Amblyrhynchus. Two molar teeth of Ameiva. 



The teeth of Iguana are serrate and acuminate, bat if they were 

 supposed to lose the acuminate character by all the denticles growing 

 to the same height from a depressed base, then the parallel vertical 

 serrations would reproduce the incisors of Galeopithecus ; and that 

 the incisors have originated in some such way is suggested by the 

 premolars in that genus being acuminate and serrated. The grooved 

 tooth of Plagiaulax and Hypsiprymnus is equally suggestive of the 

 origin of complicated molars from a simpler form such as may be 

 found in reptiles. It is well to remember, as showing how difficult it 

 is to recognise class characters in the form of a tooth crown, that a 

 naturalist so familiar with mammals as de Blainville was of opinion 

 that the small mammalian jaws from Stonesfield, known as Amphi- 

 therium, were the jaws of reptiles before Sir R. Owen demonstrated 

 that the molar teeth possessed two roots. But whether the molar 

 teeth of mammals wei*e evolved out of simple reptilian types of teeth 

 such as have been discussed as consequences of other changes in the 

 skull, or are due to the influence of habitual food on inherited struc- 

 ture, it is to be anticipated that the primitive mammals possessed 

 I teeth of reptilian type, less differentiated than the molar teeth of 

 some existing lizards. 



