606 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 5 



It would explain the occurrence of Microphrys aculeatus at such localities 

 as Tagus Cove, Academy Bay, and South Seymour Island, since all are 

 within the zone of influence of cold current B. Likewise, taking Wen- 

 man Island as a starting point, such a scheme would account for the 

 present known distribution of most Gulf of California species in the 

 Galapagos Islands. It would explain the occurrence of Piluinmis xantusii 

 at Albemarle Point and James Island, and of Eurytium affine at Conway 

 Bay, north shore of Indefatigable Island, since these are within the zone 

 of influence of warm current A. Only the finding of Lcptodius occi- 

 dentalis at Hood Island in 1925, as recorded by Boone (1927) is incom- 

 patible with this scheme. In order to appreciate the significance of the 

 occurrence of this Gulf of California littoral species at the most southerly 

 island of the group, and to understand the manner in which Gulf of 

 California and Peruvian species may have reached the outposts of the 

 Galapagos archipelago, it is necessary to consider the general scheme of 

 circulation of ocean currents in the Eastern Tropical Pacific. 



OCEAN CURRENTS 

 (Charts IV-VII) 



The accompanying Chart, IV, compiled from various sources, shows 

 that four ocean currents are concerned in the movement of water masses 

 in the region bounded by the Gulf of California on the north, the coast 

 of Peru on the south, and the Bay of Panama on the east. These are the 

 California Current, the Equatorial Countercurrent, the Nifio Current, 

 and the Peruvian or Humboldt Current. 



The California current sweeps down the west coast of Lower Cali- 

 fornia, turning southwestward off Cape San Lucas, rather than con- 

 tinuing down the coast of Mexico, part of it becoming the westwardl}^- 

 directed North Equatorial Current. Two thousand miles or more off- 

 shore it impinges upon the Equatorial Countercurrent, which is traveling 

 in almost the opposite direction, due east. Upon reaching the mainland 

 of Central America a portion of this current turns northward and west- 

 ward along the Mexican coast, and a portion is deflected southward and 

 eastward to join the Nifio Current of the Bay of Panama. 



The Nino Current is normally found only as far south as Punta Santa 

 Elena, Ecuador. Its waters are warm, 86° F. being an observed surface 

 temperature. Average salinity is said to be 33.00 o/oo (Sverdrup, 1942, 

 p. 705). Seasonally, from January to April, it extends its influence 

 southward, meeting the northerly-directed Peruvian Coastal Current at a 

 point south of Guayaquil and deflecting it away from the coast of South 

 America. 



