133 
Hooker. — On . P achy theca. 
testa is thick, homogeneous, formed of fibres or elongated cells 
perpendicular to the surface ; and that these fibres appeared 
in the specimen to be intermixed with globular cells, possibly 
in consequence of alteration of the tissues. Sir J. W. Dawson 
goes on to say that this is precisely the appearance presented 
by the testa P achy theca ; that Brongniart’s Aetheotesta is un- 
doubtedly a seed, and that the latter author compares it with 
the nut-like seeds of Taxineae. Sir J. W. Dawson concludes 
by saying that, as Pachytheca has been found in both England 
and North America associated with Prototaxites , and since the 
structure of the Corwen specimen of P achy theca corresponds 
with that of Prototaxites, the presumption becomes strong that 
the connection is not accidental, and considering the Taxine 
affinities of Aetheotesta, Pachytheca affords some corroboration 
of the gymnosperm nature of Prototaxites. 
In the discussion that followed the reading of Sir J. W. 
Dawson's paper Mr. Carruthers stated that he thought I was 
justified in referring the carbonised specimens of Pachytheca , 
which I had first seen, to Lycopodiaceae ; but having himself 
examined beautifully-prepared sections of Pachytheca , and 
found the cellular structure filling its interior, he was inclined 
to doubt its being really a vegetable, and wished that zoologists 
would examine it. 
Mr. Carruthers was followed by Dr. Martin Duncan, who 
did not regard the central part of Pachytheca as a mycelium, 
but regarded the whole organism as the float or conceptacle of 
a seaweed. 
Mr. Dyer’s letter accompanying my specimen was then 
read, in which he said that he had come to the conclusion that 
the structure of Pachytheca agreed in general plan with that 
of Codium , but with the peripheral walls branched instead of 
simple : and that Prototaxites and Pachytheca are referable to 
the same morphological type of structure ; but that there is no 
evidence of the latter being a sporangial organ of the former. 
He further stated that the radiating cells of Pachytheca ter- 
minated in the loosely-interlacing, slender filaments of the 
central cavity. This organic connection between the tissue of, 
