146 Barber . — The Structure of P achy theca. II. 
(3) a zone of dubious nature, uniting the two, called the zone 
of oval bodies. 
The relation between the cortical and medullary tubes 
could not be determined, and the zone of oval bodies was 
unexplained. It is hoped that in the present paper both of 
these difficulties will be removed. 
Comparatively recently, I have had the good fortune, by 
the kindness of Mr. John Storrie, Curator of the Cardiff 
Museum, to come across a valuable series of Pachytheca 
slides ; and it is with these that I propose to deal in the 
present paper. 
The specimens, from which the slides were prepared, occur 
in a small, isolated portion of Silurian rocks in the neighbour- 
hood of Cardiff. These have been determined by Professor 
Sollas to comprise layers between the Old Red Sandstone 
and rocks of Lower Wenlock age ; and it is in the lower part 
of the series that Pachytheca is found. 
The Wenlock beds are well exposed in the Tymawr quarry, 
a conspicuous object on the right of the road leading to 
Newport. There are several beds in which Pachytheca occurs. 
In the uppermost one, which I have carefully examined, there 
are a great number of pieces of Nematophycus , and a fair 
sprinkling of Pachytheca : all seeming to be more or less 
rolled or waterworn. 
The specimens of Pachytheca are usually perfectly spherical, 
and sometimes very hard. They seem to consist of an exceed- 
ingly fine argillaceous matrix in which many of the structural 
details have been preserved. Mr. Storrie has collected the 
specimens of Pachytheca and N ematophycus^ for a number of 
years past, and has himself prepared an exceedingly interesting 
series of sections. These he has exhibited at various local 
scientific gatherings, and has now placed them at my disposal 
for description. 
1 The specimens of Nematophycus are, if anything, better preserved than those of 
Pachytheca ; and I hope, at some time, to publish a paper on the former, since the 
plant found at Cardiff appears, in certain particulars, to differ from the Canadian 
specimens kindly sent me by Sir William Dawson. 
