562 TEST ACE A ATLANTIC A. 



There cannot be much question that our knowledge of the 

 Land-Shells is still very imperfect for some of the archipelagos 

 which are included in this memoir. This is notably the case 

 with that of the Cape Verdes, which can scarcely be regarded as 

 more than fragmentary ; and there is clearly, also, much yet to 

 be done in the Azorean Group. The Madeiras have un- 

 doubtedly had the greatest attention bestowed upon them ; 

 but, apart from this fact, the truly ' Atlantic ' element may be 

 said to attain its maximum in that particular cluster, — which 

 is more densely stocked with types not only of a more isolated 

 and peculiar character than is the case in the other islands, but 

 apparently quite aboriginal. At the Canaries a wide field still 

 remains practically to be investigated ; yet the recent researches 

 of many naturalists have contributed largely to the information 

 which has been accumulating gradually concerning them. True 

 it is that the absolute species which have hitherto been detected 

 there are not fewer than those which have been brought to light 

 in the Madeiran archipelago — being, in point of fact, a little in 

 advance ; but then the superficial area over which they range is 

 very much more extensive, and the altitude of the mountains 

 (the Peak of Tenerifife being upwards of 12,000 feet above the 

 sea) is considerably greater, — so that a nearly equal number of 

 specific modifications in the two Groups does not by any means 

 imply an equal redundancy in their faunas ; added to which, we 

 have not the same array, at the Canaries, of the varietal de- 

 velopments (hardly less significant than the actual ' species ') 

 which constitute so marked a feature at the Madeiras. As for 

 St. Helena, which is but a single island and in a state of great 

 deterioration, there is every reason to suspect that the species 

 which have been ascertained to occur there (and principally in 

 a subfossil condition) will never be very materially augmented ; 

 though perhaps, when the deposits which contain the shells, 

 more or less semifossilized (and which must have lived at a 

 comparatively recent period), have been more fully examined, 

 the extinct fauna may still be increased by a few stray members. 

 A glance f>t the general catalogue will shew that, up to the 

 present date, the forms, in the respective archipelagos, which I 

 have looked upon as specific ones are embodied in the following 

 numbers: — 



