1918. ] Dolium variegatum Lamarck at Maskat. 451 
of a certain geological horizon in a particular region, replaced 
by another fauna, and reappearing as the result of a supposed 
immigration from some other area where it had in the 
meantime survived. The more characteristic of those in- 
stances have now been shown to rest upon misinterpretations of 
the stratigraphy, the “colony ” being truly synchronous with 
t ‘ 
from one another, belong to the class of “ equivalence” or 
living shell at Maskat and Karachi affords a possible clue to 
the observed instances in which species, at present restricted 
to the southern hemisphere, are found in a fossil state in the 
f Indi 
n 
Tertiary fauna of Australia is still too fragmentary to verity 
whether it already existed in that region in Tertiary times; 
ut its occurrence in a fossil condition in Java south of the 
to the ustralian region ; while its occurrence, in the M 
1 beds of the same age as those yielding the same fossil 
that, at th period, it also ranged across the intervening 
th *6 € may admit therefore that it is practically ae 
at Jn Tertiary times Dolium variegatum rang rom tne 
"Migrated ” thence i ite directi rds t 
eas n opposite directions towa ‘ 
st and north-west. Tie fn of its geological history now 
