WATSON : RELATION OF MADEIRAN MOLLUSCA TO OTHERS. 5 



character are found at a high level on the Desertas presenting 

 specimens few in number but of very interesting species — also 

 semi-fossil like those previously referred to. In these beds there- 

 fore, geologically recent but chronologically of great anciquity ; 

 parted from us, as they are, by a period whose minimum is five 

 hundred years, a record is preserved quite undisturbed, enabling 

 us to compare the earlier Terrestrial mollusca with those now 

 alive. Following up then, such a comparison, the one hundred 

 and thirty-three genuine Terrestrial mollusca peculiar to Madeira 

 fall into three groups : — 



1. The extinct subfossil species. 



2. The surviving subfossil species. 



3. Living species that are peculiar indeed but not subfossil. 

 Of the ist class, comprising the extinct subfossil species, 



there are twelve. 



Of the 2nd group, including the species which are subfossil 

 but which are also living still, there are sixty-four. 



Of the 3rd, which contains species living, but not subfossil, 

 there are fifty-seven. 



The record is a long and a crowded one — long, for it begins 

 more, probably very much more, than five hundred years ago — 

 crowded, for it speaks of at least seventy-six (i.e. 12 -F 64) species 

 — all peculiar — many very abundant. From nowhere outside 

 did they come to these islands, but from untold ages previously 

 they may have existed on this spot. Of these seventy-six, 

 twelve species have died out, and sixty-four survive to this 

 present, while fifty-seven species more, not found among these 

 fossils, have come on the scene, and are alive now. Across the 

 page one hundred and thirty-three lines are drawn. Of these, 

 twelve — present where the record begins — break short, they 

 do not come down to our day ; sixty-four, which begin as early, 

 still run on to the present time — and fifty-seven make their 

 appearance. They may have been alive in the earlier period, 

 but they are at least not recorded there. 



