- 15 - 



geographical position of the deposits that have heel the 



faiiiia; ;;"et this aspect is emphasised in a striking imnner hy 

 the extreme development of certain groaps and the ahsence of' 

 others that are prominent in the Tertiary- faunas of the At- 

 lantic Oos.st. A mere glance at the faunal lis'; shov;, '■'-■- 1 the 

 most prolific genera. Area , Pec ten , Phacoid es, Oar^j_ij^ and 

 Jellina are characteristically tropical or are represented onlj 

 b^ sections or s:^ecies that are confined to lo- "• '"itudes or 

 there reach their mazimtun development. Aocording to the latest 

 faimal lists only t'TO of th 18 oecies that -oe raits to the 

 riecent at the ■ore^.ci.;. ui.-c -"-r'^-g ^'^r-'rh of >'"■"- "atteras, the 

 uhiqrdtous Anomia simplex and Pi varicella g-gadrisulc ata ; eight 

 are found from Hatteras southward to the V/est Indies or Brazil; 

 seven are confii'ied 'jo the area south of Florida and one soecies 

 is restricted to' the tropical porti :ns of the '.Vest Coast. 

 Virtually the same proportions obtain for a la-i.'~e nuxjber of 

 recent species that are closely related to certain Bovvden forms. 



One of the most striking features of the fauna is the 

 lUiUsual develooment of the Areas, a /lat attains its 



greatest irapor ta-ic e in the wnrmer l' e ,; . The species are such 

 as might he e::pected in tropical waters; indeed a number of them 

 are encountered in the --iresent Test Indian fau. . ^he genus 

 Pecten is usually a conopioaous element in Ter"'""''"" '~'"'^ ^ece'nt 

 faiiTiSS of almost all latitudes, but the ]a.rge species that are 



