LAND AND BRACKISH WATER MOLLUSCA 

 OF COCOS ISLAND 



By 



G. Dallas Hanna and Leo George Hertlein 

 California Academy of Sciences, San Francisco, California 



The collections upon which this paper is based were made by mem- 

 bers of the Expedition of the California Academy of Sciences to the 

 Galapagos Islands in 1905-1906;^ by the junior author during an expe- 

 dition to the Galapagos Islands in Captain G. Allan Hancock's motor 

 cruiser, Velero III, in 1931-1932;- and by members of the Templeton 

 Crocker Expedition of the California Academy of Sciences in 1932.^ 



Cocos Island^ lies in 5°32'57'' N. Lat., 86°59'17'' W. Long., about 

 half way between the Galapagos Islands and the Central American 

 coast. Politically, it belongs to Costa Rica. The island is about 500 

 kilometers from the mainland. It is composed, at least for the most 

 part, of volcanic agglomerate and other volcanic rocks. The circumfer- 

 ence is about 23.3 kilometers (about 13 nautical miles or 14.6 land 

 miles) and the area is approximately 46.6 square kilometers. The highest 

 point of elevation is in the western part of the island and has been 

 reported^ to reach a height of 849.8 meters (2,788 feet). There is 

 much rainfall and the largest stream, which flows into Wafer Bay, is in 

 the Arroyo del Genio. The coast is abrupt at many places and there 



1 Slevin, J. R., Log of the Schooner Academy on a voyage of Scientific 

 Research to the Galapagos Islands, 1905-1906. California Academy of Sciences, 

 Occasional Paper 17, 1931, 162 pp., 17 pis. [General account.] 



- For a general account of this Expedition see: Sam T. Clover, A Pioneer 

 Heritage. Los Angeles, California, 1932. Saturday Night Publishing Co., pp. 1, 

 II, 1-291. 97 pis., 4 maps. 1 text figure. See especially pp. 182-218 and map 

 showing itinerary and route, inside front cover. 



3 Grunsky, C. E. The Templeton Crocker Expedition of the California 

 Academy of Sciences, 1932. Foreword, Proc. Calif. Acad. Sci., ser. 4, vol. 21, 

 no. 1, March 14, 1933, pp. 1-2. Introductory statement by Templeton Crocker, 



pp. 3-9, pi. 1. Hanna, G. D., Science, vol. 76, no. 1974, October 28, 



1932, pp. 375-377. 



4 See handbooks prepared under the direction of the Historical Section of 



the Foreign Office, London, vol. 22, no. 141, 1920, pp. 7-30. Campbell, 



M. Searching for Treasure in Cocos Island. New York, 1932. Frederick A. 

 Stokes Co., VIII, 279 pp., frontispiece colored, 4 pis. 



5 South America Pilot, H. O. no. 174, Ed. 2, vol. 3, 1920, p. 405. 



Mexico and Central America Pilot (West Coast), H. O. no. 84, Ed. 7, 1928, p. 69. 



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