NO. 8 HANNA AND HERTLEIN : MOLLUSCA 125 



references to these works are found under various species in the follow- 

 ing pages. 



After reducing some of the names to synonymy we are able to recog- 

 nize only five definitely endemic species of land snails from the island. 

 Two others, an Opens and a Leptinaria, may have been introduced. The 

 endemic forms belong to the genera Ochrodermella, Nesopupa, Succinea, 

 and Guppya. The representatives of all except the last have their closest 

 relatives in Polynesia. All of the species are rather inconspicuous and 

 this makes the anomaly in distribution the more difficult to explain. It 

 hardly seems possible that collectors would have missed getting some 

 representatives of the rich Central American or Galapagan faunas if 

 they were present. Therefore we are forced to admit, for the present, 

 the Polynesian affinities of the land shells. This conclusion is in agree- 

 ment with the opinion expressed by Kobelt, who explained the Poly- 

 nesian affinities of the land snails as being due to the eastward direction 

 of the equatorial countercurrent which flows past Cocos Island. It 

 should be mentioned that all of the species of land snails recorded herein 

 have been secured on the lower levels of the island. It seems possible 

 from conditions found elsewhere that there may be others at higher 

 elevations. 



The four brackish water species listed herein, belonging to Auricula 

 and Melarnpus, wide-ranging tropical genera, are of no great value in 

 deciphering the origin of insular faunas. They have been determined 

 as forms which also inhabit the adjacent coast of the mainland, some 

 500 kilometers to the east. 



Siphonaria gigas Sowerby and its variety characteristica Reeve, and 

 Neritina pilsbryi Tr\'on (referred to as N. latissima var. globosa 

 Broderip, by von Martens, and Biolley) occur at Cocos Island, but 

 these have been placed with the marine mollusks in the faunal lists of 

 Cocos Island. 



Ochrodermella cumingiana (Pfeilifer) 



Tornatellina cumingiana Pfeiffer, Proc. Zool. Soc, London, January- 

 June, 1850, p. 134. "Real Llejos (H. Cuming)" [Nicaragua]. 

 —Pfeiffer, Conchyl.-Cab., vol. 1, abt. 15, 1841-1855, Pupa, p. 

 148, pi. 18, figs. 6, 7.— Pfeiffer, IMonogr. Helic. Viv., vol. 3, 



1853, p. 525. von Martens, Biol. Centrali-Americana, 



Moll., 1898, p. 324. von Martens, in Albers, Die Helic, 



ed. 2, 1860, p. 260. Kobelt, Nach. Deutsch. Malak. Ges., 



Jahrg. 31, 1899, p. 27. Cocos Island. 



