226 Transactions. — Zoology. 



salt water could have passed over the vast tracts of ocean 

 which frequently separate their present habitats from the 

 nearest continental areas in which closely-allied forms are 

 found. Nevertheless, the fact that such islands as New Zea- 

 land, the Sandwich Group, the Canaries, the Cape de Verde 

 Islands, St. Helena, and others equally remote from conti- 

 nental lands, possess numbers of endemic forms shows that 

 the means of dispersal, whatever these may have been, were 

 sufficient to bring about their occupation by a large variety of 

 forms in this particular group of animals. 



In connection with these facts attention has been pointedly 

 called to the circumstance that the forms of land-shells are 

 very stable, and that they have, indeed, continued with little 

 change through many geological periods, and therefore that 

 time must be treated as a most important factor in bringing 

 about the distribution which we now find to exist. As an 

 instance of this stability of form, Wallace has pointed out 

 that most of the land-shells found in the Miocene and Pliocene 

 formations in England are similar to, and many of them 

 almost identical with, species still living in England ; that, in 

 the Eocene, ordinary forms of many of the existing genera, 

 especially of Helix, Clausilia, Pupa, Bulimus, Glandina, 

 Cyclostoma, Planorhis, Paludina, and Limncea, have been met 

 with, and he specially mentions that one species of Helix 

 found in the British Eocene is still living in Texas, whilst 

 some of the existing Brazilian sub-genera have been found in 

 a fossil condition in Eocene strata in the south of France ; and 

 he further mentions, as a still greater proof of the stability of 

 this group, the recent discovery, in the coal-measures of Nova 

 Scotia, of two species of Helicidce, both of living genera, some 

 specimens of which were obtained from the hollow trunk of a 

 Sigillaria, and others, in large quantities, in a bed full of 

 stigmarian rootlets, and he adds that between the shells so 

 found and living species of the same genera the most minute 

 examination has failed to detect the slightest difference inform 

 or microscopic structure. Looking to these facts he points out 

 that, in estimating the importance of peculiarities or anomalies 

 in the continued existence and geographical distribution of the 

 present living land-shells, as compared with that of many of 

 the higher forms of life, we must always bear in mind the 

 possible and even probable higher antiquity of the former. 



I have already mentioned all that is at present known of 

 the local distribution of the specimens of Paryphanta now 

 before you, but this peculiarity is merely analogous to that of 

 some of the other forms of life, both animal and vegetable, in 

 these Islands. Amongst our birds, for example, you will at 

 once call to mind the restricted ranges of the huia, of Nestor 

 notabilis, and of some other species. In our plant- life it 



