30I Costa Rica Miocene— Olsson 29 



Flcurotoma alesidota Dall var. 



magma Bose Dn/Ha cojisors Sowerby, Gatun 



Conns Agassi zi Dall variety 



ninltiliratus Bose Conns multiliratus Bose, Gatun 



Conus Burckharti Bose Gatun 



The above species are from Tuxtepec and Santa Rosa. To 

 these we may add, from Barranca de Santa Maria Tatetla, the 

 following forms: 



Ostrea sculpturata Conrad Ostrea costaricensis Olsson, Gatun 



Ln-cina qzcadrisulcata L,inne Divaricella quadrisiilcata d'Orb 



Gatun, Upper Chesapeake Miocene to 

 recent 



LcEvicardiinn serratmn 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. However, ' it shows the close relationship be- 

 tween these Mexican species and those of the Gatun and the 

 Bowden, such as Sco7isia sublcsvio-ata , Phos mcxicaniis, Co7ivs 

 multiliratus and others, with a few typical Chesapeake species 

 such as Chione ulocyma Dall, Dosinia acetabulu7n Conrad and 

 Cardium sublineatuvi Conrad. This illustrates the interming- 

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

 peake, and proves their equivalence in age. 



Thk East Coast Miocene 



A fine development of Miocene rocks is found along the 

 Atlantic coastal plain and they extend more or less continuously 

 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 j-ouuger forma- 

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

 cene beds are divisible into two series, which earh^ were classifi- 

 ed as (a) the older or sub-tropical Miocene and (b) the j^ounger 

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

 main faunal differences. The upper division consisting of sever- 



