201 



Costa Rica Miocene— OLvSson 



29 



Pleurotoma alesidota Dall var, 



■magma Bose Drillia consors Sowerby, Gatun 



Co fins Agassi zi Dall variety 



multiliratus Bose Conns mnltiliratiis Bc^se, Gatun 



Conus Burckharti Bose Gatun 



The above species are from Tuxtepec and Santa Rosa. To 

 these Vv^e may add, from Barranca de Santa Maria Tatetla, the 

 following forms: 



Ostrea sailptnrata Conrad Ostrca costariceiisis Olsson, Gatun 



LiLcina quadrisulcata Ivinne Divaricella quadrisiilcata d'Orb 



Gatun, Upper Chesapeake Miocene to 

 recent 



Lcsvicai'dimn serratum Linne.. Gatun, Upper Chesapeake to recent 



Dosinia acetabulum Conrad Gatun - Chesapeake Miocene 



The above list is but a partial one of the entire fauna from 

 these localities. Howev^er, it shows the close relationship be- 

 tween these Mexican species and those of the Gatun and the 

 Bowden, such as Scoyisin sublcsvigata, Phos 77i('xuc7n:s, Cc7iv.s 

 multiliraiiis and others, with a few typical Chesapeake species 

 such as Chione idorynia Dall, Dosinia acetcCoulu^n Conrad and 

 Cardiu7n subliiieatuiu Conrad. This illustrates the interming- 

 ling of the Gatun- Bowden- Gurabo fauna with that of the Chesa- 

 peake, and proves their equivalence in age. 



The East Coast Miocene 



A fine development of Miocene rocks is found along the 

 Atlantic coastal plain and the}^ extend more or less continuoush^ 

 from New Jerse}- south into Florida. They are continued around 

 the borders of the Gulf of Mexico into Texas, but in these re- 

 gions, their marine phases are deeply covered by 3-ounger forma- 

 tions, and they are knovv^n only from deep wells. These Mio- 

 cene beds are divisible into tv/o series, which earl}^ v/ere classifi- 

 ed as (a) the older or sub-tropical Miocene and (b) the younger 

 and cold-water Miocene. These terms are descriptive of their 

 main faunal differences. The upper division consisting of sever- 



