TEETH OF DIPHYODONTS. 



303 



The views of the nature of these teeth, as given in the foregoing 

 description, are expressed by the following formula :- 



.3.3 



1.1 



6.6 



m - - = 40. 



241 



'3.3 5 ^2.2 5 "5.5 



The small insectivorous mammal, called Spalacotherium , which 

 has left its fossil remains in the upper Oolite of Purbeck, had ten 

 molar teeth on each side of the lower jaw, of which six at least 

 presented a tricuspid crown with proportions very similar to those 

 of the Chrysochlore. 



In the Shrew-moles of America (Scalops) the dentition makes 

 an important step towards the normal mammalian condition, by 

 the restriction of the characters of the true molar teeth to the 

 three posterior ones in each lateral series. Between these and the 

 large scalpriform incisor, in the upper jaw, there are six teeth, 

 the first two of which must also be regarded, by the analogy of 

 the Chrysochlore, as incisors ; the next tooth might pass for a 

 canine ; and the remaining three for premolars : of these the last 

 is the largest, and has a triedral pointed crown. The true molars 

 have large crowns, each with 

 six cusps, four on the outer, 

 and two on the inner part of 

 the grinding surface. In the 

 lower jaw the first incisor is 

 small and procumbent, and 

 the second large and lani- 

 ariform ; the third is absent, 

 and a vacant space separates 

 the incisors from the three 

 premolars, and the crown 

 of each true molar consists 

 of two parallel three-sided 

 prisms, each terminated by 

 three cusps, and having one 

 of the angles turned out- 

 ward, and one of the faces 

 inward. The dental formula 

 of this genus, according to 

 the above description, is 



. 3.3 ^ 1.1 3.3 3.3 



n QJO 



2.2' 



1.1 3.3 



7-1 _ 



' P 3.3' 



3.3 



= 36. 



Dentition of Mole (Talpa). 



The dentition of the common Mole (Talpa europcea), fig. 241, 

 includes eleven teeth on each side of both upper and lower 



