130 Scott and Maslen . — The Structure of Trigonocarpus. 
the beak is represented by a furrow with a median groove, because the actual 
micropylar beak has been broken off and only its impression remains. 
The body of the seed shown in Fig. 17 presents much the same appear- 
ance as that of Fig. 16 ; what appears to be the sclerotesta is shown at s.t., 
while c is perhaps the surface of the coaly shale which forms a cast of the 
interior cavity. A fact which is difficult of explanation, on the supposition 
that c in Figs. 16 and 17 represents the surface of an internal cast of the 
cavity of the seed, is the complete absence of any sign of the longitudinal 
ridges which are so characteristic a feature of the ordinary sandstone internal 
casts of Trigonocarpus. Mr. E. A. Newell Arber informs us that he has 
seen hundreds of such smooth specimens. The absence of longitudinal 
ridges would be equally difficult to explain if we assume that the smooth 
surface c represents the surface of the whole seed squashed flat, for we 
should expect the sclerotestal ridges of the body of the seed to be shown. 
The most interesting feature of the specimen shown in PI. XII, Fig. 17, 
is the impression of the sarcotesta, sa., which surrounds the whole seed and 
gives to it a regular, elongated, oval form. The whole seed may have been 
symmetrically flattened out into the form shown, or, if a real wing was 
present, it is probably seen in this specimen. On the whole, we think that 
the specimens shown in Figs. 16 and 17 favour the presence of a real wing, 
although the evidence from the impressions, as well as from the study of 
the petrified specimens, is not conclusive. 
The third of our figured specimens of Carpolithes alata ( Trigonocarpus 
Parkinsoni ?) is shown in PI. XIII, Fig. 18, the magnification being equal 
to that. of the others. The specimen comes from Jarrow, and belongs to 
the Hutton Collection in the Newcastle Museum. The total length of the 
seed as shown is about 4 cm., the body of the seed being i-8 cm. and the 
micropylar beak 2-2 cm. in length, while the maximum width of the body is 
1 *5 cm. The size is therefore approximately equal to that of the other two 
impressions and to the ordinary petrified specimens. The micropylar beak, 
in.b ., has a triangular form, and tapers rather rapidly above. The body of 
the seed and the micropylar beak are apparently represented as internal 
casts in the coaly shale. One of the internal grooves of the sclerotesta is 
represented by the conspicuous ridge, r., which is seen passing across the body 
of the seed, and continuing as the prominent edge of the triangular micro- 
pyle and traceable almost to the summit of the latter. That the surface of the 
body of the seed shown is really that of an internal cast, and not the outer sur- 
face of the sclerotesta, is clear from the fact that but one longitudinal ridge can 
be seen either here or along the micropylar tube. Preservation of the outer 
surface of the sclerotesta sufficiently good to show one well-marked ridge 
would be practically certain to show others also. Moreover, the sclerotesta 
itself is seen in this specimen as a layer of coaly material, sJ., which encloses the 
internal cast in places, although the greater part of it has been broken away, 
