128 Scott and Mas ten, — The Structure of T rigonocarpus. 
triangular micropylar tube had broken off. Many of the specimens also 
show a circular or oval scar at the lower or more rounded end ; this scar 
probably indicates the edge of the tracheal disk from which the free nucellus 
sprang (see PI. XII, Fig. 12,/.). The internal casts show, as a rule, three 
well-marked longitudinal ridges, which doubtless represent the three 
longitudinal furrows on the inner side of the sclerotesta of Trigonocarpus 
Parkinsoni. We have described (p. 108) how these furrows become less 
deep or pronounced towards the base of the body of the seed in petrified 
specimens ; it is interesting to find that the internal casts show the three 
ridges dying out towards the bottom, exactly as shown in the sections. 
None of the sections of Trigonocarpus P arkinsoni which we have examined 
would yield internal casts with more than three longitudinal ridges, so that 
the casts described as Trigonocarpus Noeggerathi (Stern.), which are in size 
and shape comparable with ours, but are provided with six longitudinal 
ridges instead of three, must have belonged to a different but probably 
closely related plant. 
We pass now to the impressions shown in PI. XII, Figs. 16 and 17, 
and PI. XIII, Fig. 18, which are similar to those described by Lindley and 
Hutton as Carpolithes alata , and identified by Mr.Kidston with Trigonocarpus 
Parkinsoni l . Whether the three specimens figured here and others figured 
elsewhere all belong to the same species may perhaps be left for the present 
an open question, but that they are specimens of Trigonocarpus seems certain, 
although the correlation of the features presented by these impressions with 
the parts of the structural specimens presents considerable difficulty. 
The specimens shown in PI. XII, Figs. 16 and 17, now belong to 
the Copenhagen Museum, but were originally contained in the Hutton 
Collection at Newcastle. The specimens were obtained for us through the 
good offices of Mr. E. A. Newell Arber, F.G.S. The photographs are about 
twice the natural size, so that the total length of the specimens as preserved 
is about 4-5-5 cm. Of the total length, the rounded body of the seed forms 
about four-ninths in the specimen shown in Fig. 16, and about half of that 
shown in Fig. 17. In a figured specimen of Trigonocarpus Parkinso7iib<dong- 
ing to Mr. Kidston 2 the body of the seed forms only one-third of the total 
length. The latter specimen may represent a different species from ours, unless 
in our specimens the micropylar beak is incompletely preserved. Of the 
three examples figured in this paper (PI. XII, Figs. 16 and 17, and PL XIII, 
Fig. 18), one, Fig. 17, has every appearance of being complete at the upper 
end, but in the other specimens (Figs. 16 and 18) the micropylar beak 
quite probably extended farther than shown, especially so as we know that 
the upper portion of the beak consisted almost wholly of thin-walled, easily 
destroyed tissue. 
The specimen shown in PI. XII, Fig. 16, is probably to be interpreted 
1 Kidston (’86), pp. 218, 219. 2 Figured in Scott (’05) (i), Fig. 33, p. 146. 
