OSBORN. 



freely criticise, correct and expand this preliminary parallel and 

 the methods of attack here advocated. Realizing that an ac- 

 ceptable working basis could only be secured by cooperation I 

 drew up in 1897 a ' Trial Sheet of the Typical and Homotaxial 

 Tertiary Horizons of Europe' and circulated it abroad for criti- 

 cism. This proved to be a rather faulty trial ; extremely valu- 

 able corrections and additions were received, especially from my 

 friends Professor Gaudry, Professor v. Zittel, Professor 

 Deperet and Doctor Schlosser, Madame Pavlow, Doctor 

 BouLE, and Mr. R. Lydekker. These criticisms were em- 

 bodied in a ' Second Trial Sheet ' which was issued about April 

 15, 1898. This sheet was used as a basis for further personal 

 discussion with the above palaeontologists, also with Professor 

 Lepsius of Darmstadt, Doctor Forsyth Major of the British 

 Museum and others. In course of a tour in foreign museums, 

 I was greatly aided by many other critics, and made also nu- 

 merous observations of my own which bear upon the Holarctic 

 parallels. A 'Third Trial Sheet' is issued in connection with this 

 address ; it is probably more accurate than its predecessors but 

 it is still lacking both in the desired exactness and fullness. 

 The closer comparison of the post-Eocene divisions of the 

 Tertiary fauna of Europe and North America must be deferred 

 for a full report which is in preparation. 



I. AVAILABLE EVIDENCES OF PARALLELISM 



Among the tests of approximate synchronism of deposition 

 in the Nearctic and Palsearctic regions are the following : 



1 . Common Genera and Species : the presence of iden- 

 tical or closely allied genera and species. This time honored 

 and obvious basis of comparison is now rendered most difficult 

 by the diversity of usage in generic and specific definitions. 



2. Similar Stages of Evolution : the similarity in the 

 stage of development of allied phyla, as expressed in the pat- 

 tern of the molar teeth, in the transformation of the premolar 

 teeth, complication of the molar teeth, in the reduction of digits, 

 etc. This test of synchronism is comparatively novel. For 

 example, the remarkably definite transformation of the fourth 



