240 TEST ACE A ATLANTIC A. 



is characterized by these peculiarities that Mr. Lowe defined as 

 the ' 8. depauperata. 1 The C. deltostoma is also very unstable, 

 like certain of the Pupce, in the exact number of its volutions ; 

 and in the ' 8. depauperata ' the latter are nearly always slightly 

 less numerous, and therefore (as a consequence) relatively some- 

 what enlarged and lengthened. 



It is however in the lower and submaritime tracts that the 

 present Clausilia attains its maximum, where it is extremely 

 abundant beneath stones, and even within the crevices of the 

 walls in cultivated spots. Throughout Madeira proper and on 

 the three Desertas the specimens from such situations (although 

 more or less variable inter se) constitute, as a whole, the typical 

 ones ; and to these Mr. Lowe applied the additional distinctive 

 name of ' 8. crebristriataS They are on the average larger and 

 more solid than those which constitute the ' S. depauperata^ 

 with generally an extra whorl and the spire a trifle more at- 

 tenuated or drawn-out ; and their surface is for the most part 

 appreciably more opake, while the costse are not only less 

 densely packed together but likewise somewhat more raised. 



But the examples from the eminently dry and calcareous 

 island of Porto Santo have the characters of the normal (or 

 last-mentioned) state (as it were) unduly exaggerated, the 

 shell being, if possible, even more solid still, with the ridges 

 monstrously developed (those of them which are the most ele- 

 vated being, as a general rule, reduced in number, so as often 

 to appear exceedingly remote). This Porto-San tan race repre- 

 sents the ' a. raricosta ' of Lowe ; and it is in some instances so 

 distinct from the typical one (which abounds in Madeira and on 

 the Desertas), not merely in its greatly enlarged costse but in 

 the tumidity of its volutions, that it was proposed by Dr. Al- 

 bers as a separate species- under the title of 4 C. Lowei? That 

 it is no more however than an insular modification, peculiar to 

 Porto Santo and the small adjacent islets, there cannot I 

 imagine be any question. And, so far as its. distribution is con- 

 cerned, I may add en passant that I have myself met with it 

 on the Ilheo de Cima and the Ilheo de Baixo ; whilst from the 

 Ilheo de Ferro it was obtained by the Baron Paiva, as well as 

 from the Ilheos de Nordeste the ashy-purplish tint of the 

 examples from which induced him to apply to them the varietal 

 name of ' purpurinaS 



There is however one more phasis of this protean Clausilia 

 which stands out from the less important varieties as worthy of 

 notice, and which at first sight appears so peculiar that Mr. 

 Lowe in (1863) described it, under the name of C. obesiuscula, 

 as specifically distinct. This particular form was obtained by 

 Senhor J. M. Moniz near the Levada Debaixo, not far from 



