94 Scott and Maslen . — The Structure of Trigonocarpus . 
(2) As structureless casts and impressions showing, in addition to 
the ordinary cast of the body of the seed, the long micropyle and testa. 
(3) As completely petrified specimens in which the internal structure 
is more or less perfectly preserved. 
II. Previous Work on the British forms of Trigonocarpus. 
We propose next to pass in review the work which has previously been 
done on the British forms of Trigonocarpus , especially on the petrified 
specimens showing internal structure. The earlier papers have been referred 
to in the preceding section, but a connected, somewhat fuller account may 
be useful before passing to our own work. Lindley and Hutton, in the 
Fossil Flora 1 i deal only with the ordinary structureless internal casts, 
and with impressions showing the outer coats, but without internal struc- 
ture, which they described as Carpolithes alata. The internal casts are 
referred to several different species by differences of shape, number of 
longitudinal ridges and size. Some of these casts, T. olivaeforme and 
T. Noeggerathi , are common forms and closely resemble in size and shape 
the most commonly found petrified specimens as described in the present 
paper. These ‘ species 5 have already been discussed in this paper (p. 93). 
Other forms such as T. ovatum and A. Dawesii are less common as internal 
casts, and from their greater size and difference in shape almost certainly 
represent distinct species. 
An important paper, and the earliest one dealing with the internal 
structure of the common British form of Trigonocarpus , is that by 
Hooker and Binney published in 1885 2 . The specimens came from 
calcareous nodules in the lower part of the Lancashire Coal-field, and the 
slides are now preserved in the Geological Department of the Natural 
History Museum and in the Binney Collection at Cambridge. The authors 
give a good general account of the organization of the seed, as well as 
a short account of the relation of the petrified specimens to the common 
casts. The latter are described as being merely casts of the cavity of the 
seed, i. e. of the cavity within the hard integument. The two layers form- 
ing the coat of the seed are distinguished, and the microscopic structure of 
each described in some detail. 
The rounded (basal) end of the seed is described as being surrounded 
by an annular ridge, an outgrowth of the harder, inner, layer of the testa, 
whilst at the other end of the seed the integuments are prolonged as % 
a conical cylindrical or trigonous beak traversed by a narrow canal. The 
base of this micropylar beak is said to be surrounded, in some cases, by an 
annular ridge, but from our own observations of the original slides and 
many others of the seed, we are led to think that this appearance may 
1 Lindley and Hutton (’31-’37). 
2 Hooker and Binney (’55). 
