MADEIRAN GROUP. 153 



suring about 5 lines across the broadest part), and it is also 

 more inflated, particularly as regards the basal whorl (both 

 above and below), the upper and lower portions of its peristome 

 are more widely separated at their points of insertion, and its 

 ultimate volution is more suddenly deflected (so as to shape out 

 a more decided angle) in front. 



Both in colour and sculpture, too, the H. consors differs 

 slightly from its immediate allies,- it being more dappled, or 

 variegated, above, with irregular transverse whitish fragmentary 

 markings on either a brownish or a yellowish-brown ground, as 

 well as more or less roughened with comparatively large and 

 elongated granules (formed by the partial breaking up of the 

 coarse costate lines), which however are liable at times to 

 become evanescent. Its minute umbilical perforation, also, 

 absolutely adjoins the thickened portion of the lower lip. 



Helix calculus. 



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

 compacta, var. 0. Alb., Mai Mad, 41. t. 10. f. 19-22 



(1854) 

 ,, calculus, Paiva, Mon, Moll. Mad. 39 (1867) 



Habitat Portum Sanctum, insulamque parvam adjacent em 

 ' Ilheo de Cima' dictam ; hinc inde gregaria, sed minus fre-* 

 quens. Semifossilis rarissima. 



Like the last one, the present species is peculiar to Porto 

 Santo, where however it is both somewhat scarce and exceed- 

 ingly local ; and I think that I have met with it more abun-f 

 dantly on the small adjacent rock known as the Ilheo de Cima 

 than anywhere else. It is, however, recorded by the Baron 

 Paiva from the Pico d'Anna Ferreira, and the Pico Branco. In 

 a subfossil condition it seems to be decidedly rare. 1 



The H. calculus might well-nigh be looked upon as a large 

 and totally granulated phasis of the compacta ; nevertheless it 

 is in some respects intermediate between that species and the 

 consors, being considerably smaller than the latter, but a little 

 larger than the former. In its general aspect and its almost 

 unvariegated hue iu has certainly more in common with the 

 compacta than with the consors ; nevertheless it is both larger 

 and rather more inflated or globose than that species, its per- 

 foration is more after the exact pattern which obtains in the 



1 The Baron Paiva cites the H. calculus in a subfossil condition from the 

 Southern Deserta ; but as I have no evidence for the accuracy of that habitat, 

 and so many of the Baron's localities (and identifications) are, to say the 

 least, doubtful, I must decline, until further and more reliable information 

 has been obtained, to regard the species as otherwise than exclusively Porto-i 

 San tan. 



