THE TRIA<. 123 



with the except \mites x have disappeared 



in tl 5 types t Cycads come 



into exis not differ appreciably from 



surviving forms in mod >wth and fruiting. 



7 . Mammal. 



The oldest known mammal is found in the 



upper 1 the Trias or in the Rhsetic beds. 



There are several referred to the genus 



They arc only known from isolated 



h and are mamma the 



divided. They occur in 



Wurtemberg, and me, and VVatchet in 



The great milk tooth from Watchet 



larked with s s, like those on the ; 



:' the living -rat named 



xmnus. The animal has therefore been re- 

 ipial mammal. Animals with 

 - type of tooth at lent per 



of g a little 



tnmal named trial 



Purbeck sim- 



ilar teeth. This t. I in the genus 



found at Rheims in the lower ter- 

 :n. There is theret 

 reason to believe that very little change has taken 

 place in the oldest type of mammal since its first 

 occurrence in the Trias; and that it sen- 



tialiy a >o-rat. 



uliar marine fossils appear in the Muschel- 

 kalk. ( >ne of these is the Cephalopod shell C 

 tites, which is exactly intermediate between the 

 boniferous Goniatitcs which has the septa angu- 

 larly folded and the newer Ammonites which has 

 the folds of the septa digitated on both the front 



