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THE RANGE OF FLACOSTYLUS ; A STUDY IN 

 ANCIENT GEOGRA'PHY. 



By C. Hedley, F.L.S. 



The genus Placostt/his appears a more fruitful subject of study 

 than any other molluscan genus inhabiting the same area. Their 

 large and handsome shells have attracted the attention of the most 

 superficial and unscientific collectors; as a I'esult an extensive series 

 of them have been brought to our knowledge from remote localities. 

 Close and attentive scrutiny would scarcely justify an observer in 

 declaring that a particular minute shell did not inhabit any given 

 island, whereas a casual survey would decide whether a conspicuous 

 shell like Placostylus did or did not compose a portion of that 

 island's fauna. A larger mass of evidence, both negative and 

 positive, is therefore at our disposal in dealing with Placostylus 

 than awaits us in studying smaller species. 



The genus ranges from Faro Island, )Solomons {P. founaki), in 

 the north, to Whangarei, New Zealand (P. bovinus), in the south, 

 and from Lanthala, Fijis (P. morosus), in the east, to Lord Howe 

 Island {P. hivaricosus) in the west ; and, so far as is yet known, is 

 distributed as follows : — New Caledonia, 34 ; Solomons, 16 ; New 

 Hebrides, 3 ; Fiji, 16; New Zealand, 1; Lord Howe, 1. The area 

 of distribution of Placostylus corresponds generally to that great 

 arc of volcanic activity which stretches across the South-west 

 Pacific from the Solomons through the New Hebrides to New 

 Zealand. On either side of this earth wave extend banks to New 

 Caledonia, Fiji and Lord Howe, indented by abyssal gulfs. This 

 plateau, which for want of a better name I will call the Melanesian 

 Plateau, is probably circumscribed by the 1300 fathom zone and 

 probably the various archipelagoes upon it are connected by 

 comparatively shallow banks, but the fragmentary knowledge we 



