132 



from the first, or, in other words, that, whilst the fossil 

 deposits extend throughout the lower regions of the 

 island, far and wide, it is only in those respective por- 

 tions of the beds which join on to the present ' ' habitats ' 

 that the fossil homologues of several of the species are 

 to be met with. The H. Wollastoni is eminently a case 

 in point. That most interesting of the Madeiran Mol- 

 lusks was first detected by myself on the southern ascent 

 of the Pico de Conseilho, of Porto Santo, April 22, 1849 ; 

 and the subsequent explorations of the Rev. R. T. Lowe, 

 in conjunction with my own, have, I think, satisfactorily 

 proved that it occurs nowhere else except upon that 

 single slope. Throughout the large expanse of calcare- 

 ous incrustations which are spread over the island else- 

 where, and on the adjoining Ilheo de Baixo, all of which 

 teem with shells, I think I may assert, without fear of 

 contradiction, that the H. Wollastoni does not so much 

 as exist. Yet at the Zimbral d'Areia, which the Pico de 

 Conseilho directly overhangs, a rich tract for these 

 fossil remains, as well as in the muddy composition of 

 a cliff near at hand, it literally abounds. 



In like manner, we might recall many others which 

 are peculiar, recent and fossil, to the self-same precincts. 

 Such, for example, are the H. calculus and commiscta, 

 which swarm on the summit of the Ilheo de Baixo, in 

 both states. The H. attrita, again, is the Pico d'Anna 

 Ferreira modification of the H. polymorpha ; and it is 

 only in the beds towards the base of that mountain that 

 its fossil homologue is found. But what do these facts 



