212 TEST ACE A ATLANTIC A. 



no traces of it have yet been met with, so far as I am aware, in 

 any of the subfossiliferous deposits. Although so abundant 

 however in Madeira proper, it is remarkable that there is no 

 record of it hitherto from Porto Santo (where, nevertheless, in 

 all probability it must ' exist) ; but its occurrence on the 

 Desertas is just indicated (I think, beyond a doubt), a single 

 example having been collected by Mr. Lowe's servant on the 

 Deserta Grande c a little below the house;' and indeed I have 

 lately detected three more in a box from the Baron Paiva, pur- 

 porting to have come from that same island. And I may further 

 add that the Baron mentions its occurrence on the Southern 

 Deserta likewise. 



It is -but quite recently however (indeed only since 1866) 

 that the P. umbilicata in its strictly normal (or European) 

 aspect has been observed at Madeira, several examples having 

 been met with by the Eev. E. B. Watson at the Jardim da 

 Serra ; and this fact might seem at first sight to contradict the 

 assumption that the anconostoma is but a geographical phasis 

 of it, had we not the most positive evidence that land shells are 

 from time to time imported accidentally into the island, along 

 with consignments of plants, from more northern latitudes. I 

 feel satisfied that the contingency just referred to must be the 

 true explanation of the appearance at the Jardim da Serra of 

 the P. umbilicata in its ordinary, unaltered state ; for it is 

 well known that the late English consul at Madeira, Mr. 

 Veitch, took unusual pains to introduce plants from Eng- 

 land into his garden at the Jardim ; and the only remarkable 

 circumstance, at any rate to my mind, is, that a greater number 

 of Terrestrial Mollusks should not have found their way into the 

 island through so favourable a medium of transmission. I 

 think, therefore, that the existence of the P. umbilicata at Ma- 

 deira in both its typical and aberrant phases need not in any 

 degree predispose us to conclude that the latter (which appears 

 to me moreover to merge completely into the former) is specifi- 

 cally distinct. 



The P. umbilicata (which occurs also in the Azorean and 

 Canarian Groups, and even at St. Helena) may readily be known 

 by its pale reddish-brown, shining, frequently subpellucid sur- 

 face, its more or less elongate-ovate outline, its somewhat tumid 

 volutions, and by the single (and in the ' var. ft. anconostoma ' 

 not always very conspicuous) ventral plait of its aperture which 

 nearly adjoins the angle of its rather broadly but flatly margined 

 lip. Moreover when closely inspected it will generally be found 

 to possess very faint indications of an obsolete plait, or thicken- 

 ing, on the columella, which however is often (as in the 

 Madeiran form) so rudimentary as to be barely traceable. 



