MADEIRAN GROUP. 63 



tion, lest a too hasty analysis lead to conclusions which are un- 

 reliable, and we fail to gain a genuine estimate of the fauna of 

 that distant epoch. Moreover we must at all times be quite 

 certain that the shells upon which we may have occasion to 

 pronounce are truly subfossilised, and not merely bleached and 

 decorticated ; a consideration which makes me look with suspi- 

 cion upon many of the species which are said to have been found 

 in a subfossil condition in the other archipelagos, where the 

 deposits have not been pointed out with the same precision as 

 they have in the Madeiran Group. And so fatal indeed do I 

 consider this element of uncertainty in dealing with the ques- 

 tions arising out of the subfossil fauna that it is only from the 

 Madeiran catalogue that I shall attempt to draw any conclu- 

 sions at all upon the subject, for at any rate in the Madeiras the 

 beds have been both properly defined and systematically investi- 

 gated, and in no instances have their contents been mixed up 

 with material from other and doubtful sources. In fact so great 

 has been the desire to avoid all evidence which is untrustworthy, 

 that there are (as already intimated) but three regions in this 

 archipelago from which the subfossil forms have hitherto been 

 acknowledged as absolutely and undeniably genuine, — namely 

 ( 1 ) the island of Porto Santo, -where the deposits in question 

 (chiefly calcareous) are numerous, and widely scattered at low 

 and intermediate altitudes ; (2) near Canifal, in the east of Ma- 

 deira proper, where they slope down to well-nigh the level of 

 the sea, but nevertheless contain species many of which are of a 

 mountain character and sylvan habits ; and (3) the extreme sum- 

 mit of the Southern Deserta (or Bugio), where, although small 

 in extent, they are deep and strictly muddy. 



The following then is the list of the subfossilized species 

 which have been observed up to the present date, so far as I am 

 able to ascertain, in these three localities of the Madeiran 

 archipelago^ : — 



Pto.Sto. Mad. S. Des. 



Vitrina ruivensis, Gould 

 Hyalina crystallina, Miill. 

 Patula bifrons, Lowe . 



„ stephanophora, Desh. 



,, calathoides, Lowe . 



„ pygmrea, Drap. 



„ placida, Shuttl. 

 Helix Lowei, Fer. 



„ portosanctana, Sow. . 



' Those species to which an asterisk (*) has been added, and the names of 

 which are printed in italics, have not hitherto been met with in a recent 

 state ; and they must therefore be looked upon, until evidence to the contrary 

 has been adduced, as extinct. 



