438 Mr. C. Hedley on the Range o/Placostylus. 



and Fiji a line of soundings has been recorded of over 2000 

 fathoms, \Yhile between New Caledonia and the New Hebrides 

 two soundings of 2650 and of 2525 fathoms would indicate 

 that a gulf running south-east from the Coral Sea here inter- 

 venes. The differences between the northern and southern 

 types of PJacostylus are supplemented by other features of 

 their respective mollusk faunas. The northern type is every- 

 where accompanied by Trochomorpha, which is never asso- 

 ciated with the southern. Species of the so-called il/e/anops?'.'? 

 occur in New Zealand and in New Caledonia, but are 

 unknown in the northern archipelagoes. These scanty data 

 appear to show that early in the history of the existing fauna 

 the Melanesian Plateau was rent in twain and has never 

 since been united. 



Tlie forms of PJacostylus inhabiting the Fijis resemble in 

 shape and colour sundry of the Solomon-Island species. 

 Thus elohatus from Levuka and christovalensis from San 

 Christoval are much alike both in shape and colour-pattern, 

 and Seemanni from Kandavu finds a close parallel in Mac- 

 fa^Jandi from the Solomons. The remainder of the land- 

 mollusca of each archij)elago contribute further evidence of 

 affinity ; thus Nantna nitidissima from the Solomons resembles 

 iV. casca from Fiji ; both areas also possess a Pupina. Such 

 affinity would warrant the deduction that the Solomons were 

 the source of the Fijian molluscan fauna, though the former 

 group had probably not then received from Papua the newer 

 genera of Chloritis and Papuina. Eastwards from the 

 Melanesian Plateau Placostylus was unable to extend its 

 range ; but its derivative and representative Partula, 

 together with other Melanesian emigrants, Endodontay Torna- 

 telh'na, Helicina^ and similar minute forms, drifting east- 

 wards from island to island, colonized the oceanic groups of 

 the south-east Pacific. 



Summary. — I would remark, firstly, on the essential unity 

 of the Placostylus area as a zoological province, embracing 

 the archipelagoes of Solomon, Fiji, New Hebrides, Loyalty, 

 New Caledonia, Norfolk Island (?), Lord Howe, and New 

 Zealand — a unity explicable only on the theory that they 

 form portions of a shattered continent and are connected by 

 shallow banks, formerly dry land. This continental area I 

 propose to call the Melanesian Plateau. Secondly, that this 

 Melanesian Plateau was never connected with nor populated 

 from Australia ; probably its fauna was derived from Papua, 

 via New Britain. The presence of genera common to 

 Australia and New Zealand Is explicable on the ground that 

 they mig'cted, not from the one territory to the other, but 



