MADEIRAN GROUP. 223 



harder or more solid, the colour is darker, and the volutions are 

 very much more coarsely ribbed or striate ; added to which the 

 angle of the lip is more produced outwards into an ear-shaped 

 process, and the plaits (the lower columellary one of which is 

 usually more oblique, or less horizontal, in its direction) are 

 rather more developed. This particular state seems to attain 

 its maximum at a comparatively low elevation, and to occur 

 principally (often in company with the P. fused and recto) 

 about the roots and dead leaves of the Sempervivum tobulce- 

 forme, and a few other plants, which stud the faces of the more 

 or less dry and exposed rocks. Under such circumstances it 

 frequently abounds in the north of the island, and indeed in 

 many other districts, especially towards the coast. 



The second state (which is the ' var. /3. arboreaj Lowe) is 

 characterized by the shell being altogether thinner, paler, more 

 parallel, and much less coarsely striated ; the angle of the lip is 

 less outwardly-prominent, and the lower plait of its columella 

 is for the most part more horizontal (or less oblique). This is 

 eminently the form of a somewhat higher altitude, and one 

 which obtains more particularly within the sylvan regions 

 where its habits are mainly arboreal and subcortical. It 

 abounds, under this aspect, at the Ribeiro Frio, at S. Antonio 

 da Serra, in the Ribeira de Santa Luzia, and indeed throughout 

 the wooded districts generally. 



I am far from satisfied that these two normally opposite 

 states (namely the ' a. rupestris and the ' yS. arborea ') may not 

 in reality be specifically distinct; nevertheless since there is 

 certainly an intermediate form which appears more or less (in 

 colour, outline, and sculpture) to connect them, and since it 

 was the opinion of Mr. Lowe that they are but different aspects 

 of a single, plastic species, I will not attempt to treat them as 

 separate, deeming it sufficient, for all practical purposes, to 

 have called attention to the fact that the phases in question 

 (whether specific ones or not) are to be noted, as being in the 

 main easy to recognize. 



Under all circumstances the P. sphinctostoma is remark- 

 able for its numerous and largely developed plaits, and for the 

 extremely thickened corneous sphincter which unites the first 

 ventral one with the angle of the lip ; and it is likewise (except 

 in its aberrant, strongly-striated state) a linear, or cylindrical 

 species. 



Pupa Isevigata. 



Pupa Isevigata, Loiue, Ann. Nat. Hist, ix (1852) 

 Pfeiff., Mon. Hel. iii. 544 (1853) 



Lowe, Proc. Zool. Soc. Loud. 210 (1854) 



