MADE1RAN GROUP. 163 



bicarinata in its very much larger size, and in its volutions 

 (the ultimate one of which is not quite so deflected at the 

 aperture) being 7 in number, instead of only 6 or 6^. 



Helix vermetiformis. 



Helix vermetiformis, Lowe, Proc. Zool. Soc. Lond.186 (1854) 

 Paiva, Mon. Moll. Mad. 47 (1867) 



Habitat Portum Sanctum, in stratu conchylifero semifossilis 

 parce occurrens ; recens hodie non inventa. 



The present Helix, which has been found hitherto only in a 

 subfossil state and only in Porto Santo (where it was first 

 detected by myself at the Zimbral d'Areia), belongs to the same 

 geographical type as these immediate forms, the H. bicarinata 

 being manifestly its nearest ally. Indeed it may be said to be 

 intermediate between that species and the ' a. pererosa ' of the 

 H. turricula, being very much larger than the former, with 

 its peristome even more developed (or raised above the body- 

 volution), and with its keel perhaps, if possible, still more 

 double throughout ; whilst from the latter (which occurs only on 

 the Ilheo de Cima) it recedes in its less elevated spire, its more 

 open umbilicus, and in its surface being very much more 

 coarsely and sparingly granulated. Of the two, however, it has 

 more in common, as it seems to me, with the H. bicarinata ; 

 and indeed, when closely inspected, its characters will be per- 

 ceived to differ so little except in degree from those of that 

 species that I cannot feel at all sure that the vermetiformis (as 

 now understood) represents more than some gigantic extinct 

 phasis of it. Nevertheless since I have no vestige of connecting 

 links between the two forms, and they would appear to stand in 

 precisely the same relation to each other as the subfossil H. 

 echinoderma does to the recent H. echinulata, or as the sub- 

 fossil H. Bowdichiana and Lowei do to their living analogues 

 the H. punctulata and portosanctana (which Mr. Lowe, and 

 all subsequent monographers, have held to be, in all probability, 

 distinct), I will not attempt to treat them as otherwise than 

 specifically separate. 



The H. vermetiformis is not uncommon in the subfos- 

 siliferous beds of Porto Santo, at any rate in those towards the 

 south-eastern extremity of the island (in the direction of the 

 Ilheo de Cima). I have met with it both at the Zimbral 

 d'Areia, and in the muddy deposit of an exposed sea-cliff 

 (below the Pico dos Maparicos) to the eastward of the Villa. 



Helix turricula, 



Helix turricula, Lowe, Cambr. Phil. S. Trans, iv. 58. t. 6. 

 f. 21 (1831) 



M 2 



