68 TEST ACE A ATLANTIC A. 



Group. 1 And it is highly probable that three of even these 

 seven (namely the PatidapusiUa, the Helix erubescens, and the 

 II. paupercv/a) may have been transported from their original 

 centres along with ballast. So that we arrive at the conclusion, 

 that the archipelago, as represented by its eatfra-European Pul- 

 moniferous Gastropods, is almost ivhully independent of those 

 to the north and south of it. 



And now, to advance a step further, if we cast an eye down 

 the Madeiran list as given at the close of this section, we shall 

 perceive that, out of the 138 Terrestrial species (extra-~Euro- 

 pean) to which I have just called attention, 61 are peculiar to 

 Madeira proper, 44 to Porto Santo, and 10 to the Desertas, — 23 

 only remaining promiscuous (i. e. more or less permeating the 

 entire cluster) ; and of these 23 2 merely five 3 have been ob- 

 served as yet on all the islands. From which we infer, that 

 even withi/n the archipelago itself no great number of its Pul- 

 monata have wandered far from their particular islands, — the 

 areas of an overwhelming majority of them remaining most 

 wonderfully circumscribed. 



In making the above remarks I consider it necessary to point 

 out, that the forms on which I have relied are for the most part 

 so distinct from each other that they could scarcely fail to be 

 looked upon, by any careful and experienced naturalist, as other- 

 wise than ' species ' (technically so called). Into the abstract 

 questions of derivation and common ancestry I do not now 

 enter, — because all such problems (however ' philosophical ') are 

 at the best only speculative, and I hold that no accurate mono- 

 graph has anything whatever to do with mere speculation. The 

 truth of this becomes at once obvious from the fact, that if a 

 plausible hypothesis were allowed to be made the basis of a 

 treatise like the present one, and the species were to be reduced 

 in consequence to half the number, it would be open to any 

 future naturalist to demand a still further reduction (according 

 to the views which he happened to entertain on the qucvstio 



1 These 7 are the minute Patula plaeida and pusilla (the former of which 

 occurs likewise at the Canaries, and the latter in the Azores, Canaries, Cape 

 Verdes, and St. Helena), the Helix erubesoens and pauperoula (the former of 

 which is equally Azorean, and the latter Azorean and Canarian), the Pupa 

 mierospora 3Jid./analensis (the first of which is found both at the Azores and 

 Canaries, and the second at the Canaries), and the Lovea tornatelHna (an 

 example of which was lately detected by Mr. Watson in Grand Canary). 



" The 23 which have found their way into more than a single island are 

 the following: — Vitrina mareida, Patula Hfrons and pusilla, Helix erubesoens, 

 BowdieMana, pwictulata, rulyata, paupercula, spirorbis, leptostieta, arcta, 

 aotinophora, compaeta, abjeeta, spJuerula, and polymorpha, Pupa millegrana, 

 Clausilia deltostoma, Achatina eulvma, Lovea gracilis, tornatelHna, and mitri- 

 formis, and Oraspedopoma hteidwm. 



* Helix erubesoens, paupercula, and polymorpha, Clausilia deltostoma, and 

 Lovea mitriformis. 



