134 THE NAUTILUS. 
spite of the fact that the mountains of the smaller island are 
plainly visible from the vicinity of Canigal. Between Porto 
Santo and Madeira is deep sea, and it is evident that the islands 
could not have been united within the life-time of existing 
species of snails. Nevertheless, among the scant half-dozen 
forms common to the Canical and Porto Santo deposits is P. 
bowditchiana, one which would seem among the least likely to 
be accidentally transported across the sea. It is a heavy white 
shell, resembling in a general way the well-known Leucochroa 
candidissima of the Mediterranean basin. The vast quantities 
at Canical suggest at first a former climate very different from 
that of today, but the snail was doubtless adapted to arid or 
semiarid conditions, such as prevail now at the eastern end of 
Madeira. The sandy wastes of the locality swarm with living 
snails at the present time, but they are with inconspicuous ex- 
ceptions Helix pisana, probably introduced long ago from Africa 
by the Moors. The P. bowditchiana, however, would need more 
cover than exists now, as they were nocturnal, hiding by day, 
if we may judge by the habits of their living relatives. I have 
carefully compared the Madeira and Porto Santo P. bowditchi- 
ana, thinking that some differences might be found, but they 
are unquestionably identical. There is, however, this differ- 
ence ; the Porto Santo specimens show a much wider range of 
variation. This may be taken to indicate that the species evol- 
ved on Porto Santo, and the one or more examples which 
somehow reached Madeira started a colony which remained 
essentially true to the type represented by the immigrants. 
Twenty P. bowditchiana from Porto Santo varied as follows in 
dimensions, the first figure of each pair being the length, the 
second the diameter at right angles to the axis, both in mm. 15. 
18 (1), 15.20 (1), 16.20 (2), 17.19 (1), 18.21 (2), 2022 
21.22 (2), 21.28 (1), 22.22 (1), 22.24 (2), 23.23 (38), 24.27 
(1), 25.24 (1), 25.25(1). The shell having a length less than 
18 mm. (obtained in the vicinity of the Fonte d’ Areia) consti- 
tute a distinct form or variety, which may be named reducta. 
They are not only small, but differing from the related small 
P. punctulata, they are broadened, with a strongly and evenly 
arched outer lip, so that the whole shape is very like that of 
