rOI.I.IKR: THE SF,CTIOX PI.ACOSTYLT'S OF THE GENUS RUUMUS. 211 



ground, this is quite natural, as their specialization probably dates 

 from the separation of the islands and all means of diffusion were 

 taken away. For the Chan's, which live on trees, spreading about 

 would be more likely, but the want of large rivers, and the girth round 

 each archipelago of coral reef, form here great obstacles to their 

 dispersal by floating trees. We are, therefore, compelled to assume 

 that the development of the various species has taken place in the 

 present geographical epoch, although the root of the whole species 

 reaches back to a time in which the four island groups were connected 

 with each other more closely than now. Several species appear to be 

 extinct and are now only found fossilized, but nothing as regards 

 existence and propagation of the whole species justifies us in consider- 

 ing it as at all likely soon to be extinct. 



New Caledonia, which is the home of the large, heavy Flacostyli, is 

 an island in the South Pacific, belonging to France, and lying about 

 720 miles east-north-east of the coast of Queensland. It is about 200 

 miles in length and 30 miles in breadth. It is of volcanic origin, and 

 is traversed in the direction of its length by a range of mountains, 

 which in some cases reach the height of 8000 feet, and is surrounded 

 by sand banks and coral reefs. The coast is covered by considerable 

 tracts of forest, but the mountains are barren and I presume this is 

 the reason why most of these shells are only found near the coast. 



From specimens I exhibit you will see how thin some of the F. 

 porpJiyrostomns are until they have grown their full size, when they 

 seem to keep thickening their shells as long as they live. The sub- 

 fossil P. scmilis having an extremely thick and heavy shell. 



Thanks to the late Mr. E. L. Layard I am able to give you some 

 information about these shells that may be new to you. He wrote 

 "The Flacostyli vdiXy every 10 — -15 or 20 miles, each little sand-patch 

 of an island, in the circhng reef, will have its peculiar form or variety 

 of F. porphyrostomus for instance, and along the shore they also change. 

 This species seems confined to the sea-shore, I thought none were 

 found on the Isle of Pines, but a friend sent me a shell from there, 

 which I cannot separate well from F. porp/iyfosfo//nis, and yet it has 

 characteristics of F. fibiatus, which is the shell of that island. Its 

 varieties, too, are endless, from a dwarf of an inch or a little more 

 (var. aesopi(s) to a giant of six inches long (var. elongatjis). The Isle 

 of Pines and the Loyalty Islands seem to have a characteristic to 

 themselves and I think I could always tell a shell from them. I was 

 puzzled at getting a shell {F. edzvardsianus) from the coast of the 

 main island (New Caledonia), then it occurred to me it was the east 

 coast opposite the big island of Lifou, in the Loyalty group. Then I 

 found out the Loyalty natives, in the old days, used to land at that 

 spot to fight the New Caledonians, and, of course, they brought food 



