22. Mollusca from Juan Fernandez and Easter Island. 



NILS HJ. ODHNER, 



Stockholm. 

 With 2 plates and 24 figures in the text. 



The material upon which this paper is based was collected by the Swedish Pacific Expedition 

 1916 — 17 (director Dr. C. Skottsberg, zoologist Mr. K. Backstrom). 



I. Mollusca from the Juan Fernandez Islands. 



As regards the Mollusc fauna of these islands, the marine forms have 

 been partly investigated by PLATE, Stempell and Bergh in sFauna Chilensis», 

 1898 and 1899. The forms hitherto recorded have been included in a » Summary 

 of the littoral marine Mollusca of the Peruvian zoological Province*, published 

 by Dall in 1909 (Proc. U. S. Nat. Mus. Vol. 37). 



Dall enumerates 24 marine mollusca (incl. i Onchidmm)^ of which no 

 less than 11, or 50%, are endemic. To these, are here added 15, 9 of which 

 are described as new. The whole number of marine mollusca hitherto known 

 thus amounts to 39 species, 20 species of which, or 50 %, are endemic. These 

 are divided up among 36 genera, 2 of which are endemic, and one of them 

 established here. 



Leaving the endemic forms initially out of consideration, we find that 

 among the remaining 19 no less than 13 are common to the West coast of 

 America exclusively, 4 (PleurobrancJiaea maadata, Littorina matiritiana, Modiola 

 plume scens, and Chania hnbricata) have a distribution within the western parts 

 of the Pacific but do not reach the South American coast, and 2 (Octopus 

 tuberculatus and Modiolaria opifex) have a wide distribution within the Tropics. 

 The species common to the American coast may be divided into three groups: 

 a northern, a southern, and an intermediary one, the last one comprising those 

 with their general distribution within the Central Peruvian Province, the others 

 being more extreme to it. Most of the Juan Fernandez mollusca belong to 

 the second group; to the southern belongs e. g. Tritonia australis (the species 

 also found at Calbuco; the genus represented also in the Magellanic, but 



