ccxxvi FAUNA HAWAIIENSIS 



rendering the creatures less visible, and to be of value for protective purposes. Utterly 

 conspicuous as the shells appear when removed from their surroundings, it is quite 

 certain that, in spite of their bright colours, they are by no means so when resting on the 

 leaves or branches of trees, except for occasional specimens in incongruous positions. 

 This is quite evident from the fact that a skilled collector, with very practised eye in 

 discovering these shells, will go over the very same trees that have just been well 

 searched by one less accomplished and gather an astonishing number of shells from 

 these. The remarkable fact is that though these colour patterns must have been 

 developed on the spot, the Achatinellas would not appear to have had any need for 

 concealment. Not even once were these shells ever found within birds, nor seen to be 

 eaten by them, and it is astonishing that the thrush genus Phaeornis should not have 

 availed itself of such an abundant source of food. It is true that the introduced rats, 

 imported by man, feed eagerly on these Molluscs, so much so that I have gathered a 

 hatful of empty shells of Achatinella tesselata at the foot of a single hollow tree, into 

 which the rodents had carried them. But these cannot be supposed to have been a 

 factor in determining the colour patterns. Similarly we find the terrestrial Achati- 

 nellidae of the genus Atnastra all of dull colours and in strict harmony with their 

 environment, these being equally neglected by birds, but devoured by imported rats. 

 Either, therefore, from some unknown cause these land Mollusca become adapted m 

 colour to their environment, or if these colours have been modified and controlled by 

 causes elsewhere supposed to be efficient, this must have taken place in past ages and 

 under different faunistic conditions. In the latter case it would be natural to consider 

 the coloration, as having been determined by the ancestors of the existing species of the 

 thrushes [Phaeornis) from the Kauai form of which, on one occasion, a minute Helicine 

 shell was obtained by dissection. Further observations on Lanai and Molokai may yet 

 prove that these birds do still on occasion feed on Achatinellas ; but the numerous 

 young and old birds that I examined at various seasons gave no evidence of this, and 

 further we are perplexed by the entire absence of Phaeornis from Maui, unless we 

 suppose the genus to have once existed there and now become extinct, as we know to 

 be the case with the Phaeornis oahuensis on Oahu. 



The other genera of Achatinellidae (i.e. the true genera as distinguished from the 

 sub-genera of Achatinella itself, above mentioned) are of no less interest. 



Perdicella is a comparatively small genus of prettily marked arboreal shells. 

 P. helena is an abundant and variable species widely distributed on Molokai, but most 

 of the known forms appear to be rare or very local. It is found on the leaves of Ki, 

 Ohia and various other plants. P. niinuscula, recorded on my specimens as being found 

 on Molokai, must, I think, have been wrongly labelled, since 1 observed a species of 

 Perdicella in numbers on Urticaceous plants in the lao valley, Maui, on one occasion, 

 and collected specimens. The genus is restricted to Molokai and Maui. 



The elongate shells of the genus Newcombia are also restricted to these two 

 islands and almost to Molokai. A^. cinnamomea and allied species are found on the 



