MADEIRAN GROUP. 91 



not occur (either subfossil or recent), and there would seem to 

 be a few characters, apart from the very great dissimilarity of 

 stature, which may serve to separate the two forms. Thus the 

 H. Lowei appears to be less evidently subpunctulated (or 

 minutely asperate), even beneath a high magnifying power ; and 

 the three large fasciae which are nearly always more or less trace- 

 able on the portosanctana^ and which are at times so broadly 

 developed as to be. subconfluent, are uniformly reduced in the 

 H. Lowei (when in a sufficiently perfect condition for the colour 

 to be preserved at all) to two narrow, thread-like lines, the 

 upper cloudy band, below the suture, being obsolete. And 

 there is likewise no appearance of the H. Lowei having been 

 (like the portosanctana) infinitesimally hispid; though this 

 perhaps may be merely owing to the surface having been 

 necessarily somewhat worn, or altered, in the process of 

 decortication. 



The H. Lowei is locally abundant in many of the subfossili- 

 ferous deposits in Porto Santo, and it is also common in those 

 on the immediately adjoining Ilheo de Baixo ; but the single 

 example to which I have already alluded, as having been taken 

 by Senhor Moniz on the Ilheo de Cima, embodies the only 

 instance (so far as I am aware) in which the species has been 

 observed in a recent state. 



Helix portosanctana. 



Helix portosanctana, Sow., Zool. Journ. i. 57. t. 3. f. 5 



(1824) 

 a., Lowe, Cambr. Phil. S. Trans, iv. 46. 



t. 5. f. 15 (1831) 

 Pfeiff., Mon. Hel. i. 367 (1848) 

 Lowe, Proc. Zool. Soc. Loud. 169 



(1854) 

 Alb., Mai. Mad. 46. t. 12. f. 5-7 



(1854) 

 ., Paiva, Mon. Moll. Mad. 20 (1867) 



Habitat Portum Sanctum, insulasque parvas adjacentes; 

 sub lapidibus vulgaris. In statu semifossili minus frequens. 



As already mentioned, the H. portosanctana (which is pecu- 

 liar to Porto Santo and the immediately adjacent islets) may be 

 regarded as the modern representative of the subfossil, and com- 

 paratively gigantic, H. Lowei ; yet, for reasons which have been 

 assigned, I do not think that we possess sufficient evidence for 

 considering the two to be but altered phases of a single species. 

 The fact that both of them were members of the ancient fauna 

 (the portosanctana being then scarce, and the Lowei abundant), 



