68 T 



to the apex ol 

 if this measui 

 the age of no] 

 vical flexure ; 

 It is probable 

 the apex of tl 

 classification ( 

 sion may be 

 throughout th 

 been relativel} 

 The follow 

 to the end of 

 ratory courses, 

 to Keibel anc 

 schichte des I 

 1900. In the 

 of the various 

 It is believed t 

 to enable the 

 the desired sU 

 practically cor 

 the period of d 

 are formed. ' 

 mounts. The 

 work are no tec 



Chronoloc 



I. Before Layii 



1. Maturatic 



isthmu; 



2. Early cle 



the istb 

 membn 



3. Later cle^ 



in the 

 Data for 



II. Incubation 1 

 The period n 



of the primitive 

 (3) after the app 

 divided by time 



