THE INSECTIVORES 105 



an animal aberrant in many details and adapted it is said for 

 a fish diet, exhibits a dentition very similar to that of the 

 primitive Palaeoryctes and thus supplies an indication of the 

 correlation between the teeth of the Zalambdodonts and Di- 

 lambdodonts. The tooth formula is: 



l|.cip|,M|. total 40. 



The specimen figured has retained the first milk cheek tooth 

 in the upper jaw but it is a very useful specimen since the last 

 premolars are just erupting and all cusps are clearly shown. 

 In general the dentition and the shape of the dental arch are 

 of the usual insectivorous type and the last two premolars 

 in each jaw are increasingly molariform. Each mandibular 

 molar shows a typical trigonid with all three cusps and a hc M l 

 of fair size but low. In the upper molars a cusp not found in 

 Chrysochloris appears behind and slightly lateral to that at 

 the apex of the triangle on the palatal aspect. It is best 

 marked on the second molar. If the cusp at the apex be the 

 paracone this one must be the metacone either just budded off 

 from or fusing with the paracone. The very ancient and very 

 specialized nature of the Zalambdodont group renders difficult 

 exact comparison with the cusps of the teeth in other mam- 

 malian forms. 



