In Madeira I find in Wollaston's books a parallel case with your New Zealand case--viz., the striking absence of whole genera and orders now common in Europe, and (as I have just been hunting out) common in Europe in Miocene periods.

Of course I can offer no explanation why this or that group is absent; but if the means of introduction have been accidental, then one might expect odd proportions and absences.

When we meet, do try and make me see more clearly than I do, your reasons.
LETTER 340.

TO J.D.HOOKER.

Down, November 14th [1858].
I am heartily glad to hear that my Lyellian notes have been of the slightest use to you.