MADEIRAN GROUP. 239 



The C. crista occurs also, though sparingly, at Caui^al, in 

 a subfossil condition ; but all the examples which I have yet 

 inspected pertain to the larger form, just described as the ' var. 

 /S. decolorata;^ yet the majority of them differ from their 

 recent analogues in being a trifle more coarsely and not quite so 

 closely sculptured, — the so-called ' strise ' in some examples 

 amounting to appreciably separated, well-defined costse. In 

 spite however of the latter peculiarity (a character which is 

 eminently unstable in the Madeiran Clausilias), I cannot detect 

 anything about them to warrant their isolation as even a decided 

 ' variety.' 



Clausilia deltostoma. 



Helix deltostoma, Lowe, Cariibr. Phil. 8. Trans, iv. 65. t. 6. 



f. 37 (1831) 

 Clausilia deltostoma, Pfeiff., Mon. Hel. ii. 410 (1848) 



„ „ Lowe, Proc. Zool. Soc. Loncl. 215 



(1854) 

 „ „ et Lowei, Alb., Mai. Mad. 71. t. 16. 



f. 23-25 (1854) 

 „ obesiuscula, Lowe, Ann. Nat. Hisf.xii. 339 (1863) 

 „ deltostoma, Paiva, Mon. Moll. Mad. 142 (1867) 



Habitat ins. omnes Maderenses ; sub lapidibus vulgatissima. 

 In statu semifossili parce occurrit in Portu Sancto, necnon in 

 ins. Deserta Australi. 



This is the universal Clausilia throughout the whole 

 Madeiran archipelago, and one which is so eminently variable, 

 both in solidity and in the number and development of its 

 costse, that were it not for the intermediate links which most 

 assuredly connect them, it would be almost impossible to believe 

 that the two extremes of form (when viewed per se) could be 

 conspecific with each other. It would appear however to be 

 singularly dependent, not only upon the nature of the soil, and 

 district, in which it occurs, but likewise upon the elevation of 

 the latter, — the examples from low and arid regions towards the 

 coast being more solid in substance, and with their ridges more 

 coarsely matured (particularly when, as in Porto Santo, the 

 area of distribution is for the most part a calcareous one), than 

 those which have been collected in higher and damper locali- 

 ties further removed from the sea. Indeed it is not often that 

 the C. deltostoma ascends at all above the altitude of about 

 2500 feet ; and even the individuals from the upper limits of 

 that range are usually smaller and thinner than the others, as 

 well as more glossy and less coarsely (and more closely) sculp- 

 tured, and frequently too of a paler tint. It was the race which 



