300 PROCEEDINGS OF THE NATIONAL MUSEUM. tol. 42. 



The Pyramidellid material from the west coast of South America 

 south of Aguja Point, Peru, is exceedingly scant, too much so to 

 permit of any definite mapping of f aunal areas based upon this group 

 alone, but if we apply the same factors which are found to hold in 

 the northern hemisphere, we can say that one area (8) the Peruvic, 

 extends from Point Aguja, Peru, south to Chiloe Island, Chile. An- 

 other (9), the Magellanic, extends from Chiloe Island to the Strait 

 of Magellan, and a third (10), the Antarctic, probably covers the 

 South Shetlands, extending from there southwards. 



The faunal areas here listed show a remarkable coincidence with 

 the ocean currents in the region under discussion, which demands 

 consideration. 



First of all, it should be borne in mind that probably all the mem- 

 bers of this family are free swimming during their early stages, 

 which would render them subject to being carried by the ocean cur- 

 rents. Their future success in life after passing the free-swimming 

 stage would depend upon finding a suitable habitat for their sub- 

 sequent existence — a habitat which would embrace all the necessary 

 conditions of topography, temperature, salinity, and food supply. 

 It seems quite reasonable to suppose, and the insufficient data at 

 hand indicate, that the coasts washed by the great ocean currents 

 have in the mam a corresponding uniformity of temperature, salin- 

 ity, and food supply (plankton), the chief factors in the environ- 

 ment of marine animals. It therefore seems most reasonable to 

 assume that it is due to the dommation of these factors by the cur- 

 rents that we find the parallelism or coextensiveness of ocean cur- 

 rents and the faunal areas. 



In the North Pacific we have the Kuro Siwo or Japan current, 

 which on reaching our coast splits, the north deflection sweeping 

 the shores of Alaska and the Aleutian Islands, marking the Aleutic 

 faunal area, while the south deflection sweeps southward along the 

 coast of Washmgton, Oregon, and California, as far as Point Concep- 

 tion, where the greater part is deflected seaward, probably sweep- 

 ing the outside of San Miguel, Santa Rosa, San Nicholas, and San 

 Clemente Islands, thus outlining the Oregonic faunal area. 



A weak continuation of the main current passes southward along 

 the coast of California from Point Conception to Cape St. Lucas, 

 Lower California, where it is deflected seaward, thus covering the 

 faunal area designated as Californic. 



The equatorial current strikes the Central American coast about 

 Acajutla and passes northward into the Gulf of California, turning 

 westward at Cape St. Lucas. This maps the Mazatlanic faunal area. 



The region between Acajutla and Point Aguja, Peru, appears to be 

 free from any large ocean currents and represents the Panamic 

 faunal area. 



