296 PATAGONIAN EXPEDITIONS : PAL/EONTOLOGY. 



Glycimeris ibari. Crepidula gregaria. Murex hatcheri. 



Lucina promaucana. Natica danvitti. Marginella gracilior. 



Dosinia meridionalis. 



Miocene and Pliocene relations: i species =1.5 per cent. 



Calliostoma iheringi. 



Pliocene and Recent relations : 2 species = 3 per cent. 



Gibbula dalli. Marginella olivella. 



To sum up, among the species which may be compared with known 

 ones, the percentage of the relations with particular beds is the following : 



Cretaceous : 4 % 4 % 



Eocene 7 



Oligocene 10 



Eoc. and Olig 1.5 



Eogene 18.5.... 18.5 % 



Intermediate 12 .... 12 % 



Miocene 32 



Pliocene 6 



Recent 4 



Mioc.-Rec 19 



Mioc. and Plioc 1.5 



Plioc. and Rec 3 



Neogene 65.5....* 65.5 % 



100% 



The above figures speak for themselves. We see a constant increase 

 of the percentage from the Cretaceous to the Miocene, and then again 

 quite a sudden decrease from Miocene to Recent The percentage of all 

 Neogene forms is 65.5, considerably more than half of the number, while 

 that of the Eogene and Cretaceous together is only 22.5 ; the rest (12 per 

 cent.) is intermediate between Eogene and Neogene. 



These facts bring the Patagonian beds undoubtedly into the Neogene, 

 and when we consider the fact that after the Miocene there is a marked 

 decrease in the percentage, we must put these beds in the beginning of 

 the Neogene times, that is to say, in the Miocene. This course is ren- 

 dered the only possible one by the fact that 32 per cent, of the whole 

 number of species shows Miocene relations. No other group has a per- 



