338 THE RANGE OF PLACOSTYLUS, 



I'ecorded of over 2000 fathoms, while 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 intervenes. The differences between the northern 

 and southern types of Placostylus are supplemented by other 

 features of their respective mollusc faunas. The northern type 

 is everywhere accompanied by Trochomorflm^ which is never 

 associated with the southern. Species of the so-called Melanopsis 

 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. 



The forms of Placostylus inhabiting the Fijis resemble in 

 shape and colour sundry of the Solomon Island species. Thus 

 elobatus 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 macfarlandi from the 

 Solomons. The remainder of the land mollusca of each 

 archipelago contribute further evidence of affinity, thus Nanina 

 nitidissima from the Solomons resembles N. casca from Fiji ; both 

 areas also possess a Pwpina. Such affinity would wari'ant the 

 deduction that the Solomons were the source of the Fijian 

 moUuscan fauna ; theugh the former group had probably not then 

 received from Papua the newer genera of Chloritis and Pajmina. 

 Eastwards from the Melanesian plateau Placostylus was unable to 

 extend its range ; but its derivative and representative Partula, 

 together with other Melanesian emigrants, ^wc/oc/o^i to, Tornatellina, 

 Helicina, and similar minute forms, drifting eastwards from 

 island to island, colonised 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 I. (1), Lord Howe and New Zealand ; a unity 

 explicable only on the theory that they form portions of a 



