MADEIRAN GROUP. 155 



Mr. Lowe's ' y. portosanctana') are a trifle more flattened, with 

 the granules larger, and the costate lines (or at any rate a 'por- 

 tion of them) stronger and more elevated. And there is, in 

 addition to these, a subfossil form (which appears to be now 

 extinct) in Porto Santo, in which the stature is very much 

 reduced, the surface is almost totally ungranulated (both above 

 and below), and the umbilicus is relatively a little more open. 

 This last-mentioned phasis is the ' 8. pusillaj of Lowe. 



Helix commixta. 



Helix commixta, Lowe, Proc. Zool. Soc. Lond. 184 (1854) 

 „ abjecta, var. a., Paiva, Mori. Moll. Mad. 42 (1867) 



Habitat Portum Sanctum, pra^cipue (nisi tailor) in ins. 

 parva adjacente 'Ilheo de Baixo ' dicta ; rarior. Semifossilis 

 copiose occurit, sed tan turn sub forma ' (3. pusilla,'' Lowe, quse 

 forsan ad speciem. distinctam melius pertinet. 



At first sight this Helix might almost be mistaken for an 

 unusually depressed form of the H. abjecta, particularly the 

 4 var. j3. candisata ' of that species ; nevertheless it will be seen 

 on examination to be totally distinct, — being not only more 

 flattened or sublenticular, but with its umbilicus relatively 

 larger and more spiral, its sculpture altogether different, its 

 apex more obtuse, and its peristome more continuous, more 

 elevated, and more circular. Indeed its sculpture is exceedingly 

 peculiar, and unlike that of anything else with which we have here 

 to do, — the surface (which is of a dirty or brownish white, prac- 

 tically well-nigh colourless, and remarkably opake) being nearly 

 free from transverse costate lines (though with a few distant, 

 irregular, obtuse, subconfluent transverse folds), but densely 

 crowded with most minute sand-like granules (very accurately 

 expressed by Mr. Lowe as ' arenulato-granulosa '), which gives 

 it under a high magnifying power somewhat the appearance of 

 fine sealskin. The volutions of the H. commixta are tumid, or 

 obtusely angular, and the basal one is rather wide and strongly 

 keeled, — the keel beiDg partially caused by a very slight 

 scooping-out, or obsolete erosion, both above and below. 



The H. commixta is essentially a Porto-Santan species, and 

 I am not aware that it has been observed hitherto (as above 

 typically defined) in anything but a recent state ; though even 

 the living examples have much the colourless, calcareous 

 appearance, at first sight, of being subfossilized. There is how- 

 ever a very minutely subfossilized form (coarsely and less 

 closely granulated both above and below, nearly unkeeled, and 

 greatly resembling in its more globose outline the most diminu- 

 tive phasis of the 77. compacta) which Mr. Lowe regarded as a 



