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Mollusca from Juan Fernandez and Easter Island. 
By 
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. SkorrsBerG, zoologist Mr. K. BACKsTROM). 
tr. 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 »Fauna 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. 1 Oxchzdium), of which no 
less than II, 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 (Pleurobranchaea maculata, Littorina mauritiana, Modiola 
plumescens, and Chama imbricata) 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. 7ritonia australis (the species 
also found at Calbuco; the genus represented also in the Magellanic, but 
