128 British Association. 
southwards of his second and third barriers. This was the newer 
pliocene epoch. The period of the fifth flora was that of the post- 
tertiary, when the present aspect of things was organized. 
Adopting such a view of the relations of these floras in time, the 
greatest difficulties in the way of changes of the earth’s surface and 
destruction of barriers—deep sea being found where land (probably 
high land) was—are removed when we find that those greater 
changes must have happened during the epoch immediately subse- 
quent to the miocene period ; for we have undoubted evidence that 
elsewhere, during that epoch, the miocene sea-bed was raised 6000 
feet in the chain of Taurus, and the barriers forming the westward 
boundary of the Asiatic eocene lakes so completely annihilated, that 
a sea several hundred fathoms deep now takes their probable place. 
The changes required for the events which the author would connect 
with the peculiar distribution of the British flora are not greater than 
these. 
Prof. Forbes maintains that the peculiar distribution of endemic 
animals, especially that of the terrestrial mollusca, bears him out 
in these views. He proposes to pursue the subject in detail; with 
reference both to animal and vegetable life, in connexion with the 
researches of the geological survey. 
June 21.—‘‘ Report on the Microscopic Structure of Shells.” By 
W. B. Carpenter, M.D. 
This report formed the continuation of last year’s on the minute 
structure of the skeletons of Bivalves and Echinodermata. Dr. Car- 
penter stated that he had lately examined a recent Terebratula pre- 
served in spirits, and ascertained that the perforations in the shell, 
before described, were filled up in the livmg animal by membranous 
czeca, containing cells, forming, as he considered, a glandular appa- 
ratus, though its connexion he had not yet been able to trace. | He 
then described the structure of those bivalve mollusks in which the 
mantle is more or less closed as being generally less characteristic 
than that of the families already described, their texture being ap- 
parently more homogeneous, and the membranous residuum left: by 
the action of acid being less distinct. Frequently, however, traces 
of a cellular origin were to be seen in shells whose general texture 
was most homogeneous ; sometimes it was seen in the shell, and not 
in the decalcified membrane, and frequently m the membrane when 
no traces of it were visible in sections of the shell. Hence Dr. 
Carpenter felt himself justified in regarding all shells as originating 
in the secreting action of the cells forming the superficial layer, of 
the mantle; these cells remaining persistent and separate in some 
cases, whilst in others they coalesced. ‘The peculiar tenacity of the 
cellular membrane in Pinna and its allies was attributed to the pre- 
sence of an intercellular horny matter, between the true cell-walls ; 
the same substance being elsewhere thrown out upon the surface of 
the layer as an epidermis or periostracum. Among the shells under 
consideration in the present report, those of the family Myade were 
particularly distinguished by their evident cellular structure; the 
genus Pandora, formerly referred to as one of the most aberrant and 
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