Pvn H,i I'UitlS

PECTEX. 57
blended in specimens of P. varius and what I consider
to be its two principal varieties. Some are broader and
flatter than others : the number of ribs varies from 27
to 45 , and consequently in their comparative fineness ;
and the white of P. niveus is sometimes beautifully
tinted with purple, and passes into different shades of
other colours. I have taken P. niveus only in every
part of the Hebrides, and I have never seen a single
specimen of P. varius from that district. In Loch Fyne
and at Jura an intermediate variety occurs. A specimen
from the former locality has 36 ribs, and one from
the latter 32 ribs. I noticed in the collection of M.
Martin, at Martigues, a white variety having also 32
ribs. A still more puzzling form was sent to me in
1852 by Mr. Barlee from GlengarifF in Bantry Bay,
which clearly connects the two species; and the variety
purpurea forms another link in the chain of specific
identity. I believe this varietal difference arises from
habitat. The strong and few-ribbed P. varius lives on
oyster-banks and rough ground on an exposed coast;
while the delicate and many-ribbed P. niveus is only
found in sheltered lochs and arms of the sea, moored by
its strong byssus to the upper surface of the broad and
smooth fronds of Laminari