Ixvi FAUNA HAWAIIENSIS 



Achatinella on any one island a matter of a very prolonged period were this dependent 

 on their own movements. We once found at the foot of the Waianae slopes a number 

 of one of the terrestrial species of Amastra, quite outside the forest, hiding in the 

 hollows of a large log on the bank of a stream. This log had clearly been carried 

 down in a flood, and probably for many miles before stranding, the stream arising 

 in the Koolau range of mountains, the forest of which was miles distant. Once, on 

 Molokai, a young living Achatinella was found attached to the feathers of the Drepanid 

 bird Chlorodrepanis. Frequently they become adherent to one's clothes in passing- 

 through the brush. Doubtless in high winds very young shells are sometimes carried 

 to a distance in curled up leaves, in which they often hide. Once or twice in an open 

 treeless space on Molokai I found shells which must have been carried this way or 

 with small branches of trees during a severe gale. We have known sluggish beetles 

 of the genus Proterhiiius to be so carried far from their food-plant, doubtless only to 

 perish of starvation. 



In 1893 I took the opportunity of paying a good deal of attention to the habits 

 and distribution of some of the arboreal Achatinella on Molokai, the shells of that 

 island at the time having been less collected than those on Oahu. It was quite 

 impossible not to be struck with the effect of isolation on individuals of some of 

 these species. Achatinella macrodon (Vol. 11, PL XI, fig. 16) was very common on 

 a ridge close to my camp, but very local, for the next ridge to the west had none 

 of it, nor did I see it on any ridge in that direction. After one had crossed one or 

 two deep gulches eastward, an allied form appeared on the ridges, but with remarkable 

 variations, tending to albinism. On the first-mentioned ridge it was comparatively 

 constant, singularly so for an Achatinella. Whether it had once occupied the area 

 between these localities and subsequently died out, or whether by some such means 

 as I have indicated above, it had passed over this area, cannot be known. 



Another instance of discontinuity of distribution was examined into, over a large 

 area, in the case of the common and widely-spread Achatinella tesselata. This species 

 I found abundant over an extensive irregular plateau, where I had occasion to collect 

 often, at some distance N.W. of my camp. Here the shell was somewhat variable, 

 of good size, and a striking albinoic form occurred. On this same area nine years 

 later I found the shell much scarcer, but again the albino shells occurred. Away 

 from this area and close to my camp on one ridge only, and only on part of this 

 ridge, A. tesselata was found in large numbers, but of smaller size than the others, 

 and very uniform both in size and colour, excepting that here it was strictly dimorphic, 

 with two closely similar but easily distinguished and constant varieties. I was not 

 able to find any continuity of distribution between the two areas mentioned, in fact 

 I am sure that such did not exist. 



When we consider the sluggishness of these molluscs, it is certain that the 

 individuals of a species on two such areas, though the distance between them in 



