HYBERNIA LEUCOPHEARIA V. NIGRICARIA AT DONCASTER. 155 
Heer, par excellence the botanist of the Tertiary period, claims 
for the northern Alps in Switzerland, in middle Tertiary times, 
a mean temperature of 68°—72° F., such as now obtains at Cairo. 
No doubt one might give mean temperatures for all the past periods 
in the earth’s history, but they would be of little value even for these 
more recent and better known Tertiary beds; there are so many 
other considerations to take into account beyond the mere 
comparison of fossil and present-day species, however closely the 
two may be related. 
Starting with a subtropical or tropical climate in the Eocene 
recent English strata in company with the dwarf birch and Arctic 
willow, plants which prepare us for the swing of the pendulum to 
the other extreme, where from the Arctic regions to Central Europe 
extend slowly-spreading tongues of ice, uniting at the maximum of 
cold to form an ice-sheet almost continuous. Here and there stood 
out the higher peaks of land, oases in the ice desert, held as their 
last stronghold by a few hardy plants, as now on those peaks pene- 
trating the Greenland ice-mantle are found some few stragglers of 
the Greenland flora. 
Tempting as it is to regard plants as thermometers of past ages 
and to amuse ourselves by drawing up temperatures read by glimpses 
through the ‘corridors of time,’ interesting enough as it is to 
contrast these extinct types with their supposed living relatives, or 
to go more minutely into the subject and search with the microscope 
in transverse sections of Carboniferous trees for evidence of buried 
seasons, yet we cannot be too careful to remember we have in fossil 
plants only one link—and that, too often, an imperfect one—in the 
chain of evidence which leads us to conclusions as to climates of 
ages past. 
Daa ae 
—I have taken 
is 
Reid borgir leucop var. nigricaria at Doncaster. 
of Hybernia carmen pigs here that appears to me to be peculiar. It 
of “the following description—U pper ar ow Fore-wing, almost entirely sooty 
black slightly paler and ochreous about ise : t osta, inner : 
‘o transverse lines, rather dedi ee a trace of hind-marginal 
pale spot ing, with ee dark gray boos? surface: Entirely 
without markings, slightly nacreous, g pecs the nervures r: ve 
Only seen one of this form, or an ishing approaching to it. —H. H. Corperr, 
19, "Hallgate, Doncaster, hia an 1891. 
as I know has not previously been 
This is th 
Teported from aigkshinn Se a a of the very ng melanic forms which seem to 
occ 
ae og 
