Scott and Mas ten , — The Structure of Trigoiiocarpus. 91 
F. W. Oliver, who has commenced a re-examination of the seeds and from 
whom valuable papers have already appeared on Stephanospernium 1 , 
Trigoiiocarpus pusillus 2 , and other forms. 
In Brongniart’s memoir on these silicffied seeds from Grand’Croix, 
published in 1874 3 , they are divided into two series, according to shape, as 
follows : — 
(a) Graines a symMrie binaire , plus ou moins aplaties et bicarenPes. 
(b) Graines a symetrie rayonnante autour de P axe a trois , six , huit 
divisions ou d section circulaire. 
For these series Prof. Oliver has proposed the names Platyspermeae and 
Radiospermeae respectively 4 . 
The Radiospermeae are further divided into several groups based on the 
form of the transverse sectio , circular, triangular, hexagonal, or octagonal ; 
and the three-angled forms are referred to three genera, Trigoiiocarpus , 
Tripterosperinum , and P achy testa. Of these genera* Trigoiiocarpus and 
Tripterospermum appear to be so nearly alike as to be difficult of separation. 
Indeed, the first British specimens of Trigoiiocarpus of which the internal 
structure was described — by Hooker and Binney in 1855 5 — were regarded 
by Brongniart himself as probably belonging to his genus Tripterospermum. 
The specimens afterwards described by Williamson under the name of 
Trigonocarpon olivaeforme 6 undoubtedly represent the same form as the 
Hooker and Binney seed, and in fact nearly all the structural specimens 
which we have examined from the British Coal-Measures, and they are 
numerous, are so generally similar in size, form, and structure as to lead 
us to the conclusion that they probably belonged to the same species of 
plant. 
It is important, therefore, at the outset of our investigations, to critical ly 
consider the two genera Trigoiiocarpus and Tripterospermum , and to decide 
to which form our common British specimens should be referred. 
The characters used by Brongniart for the separation of these two 
genera are given in the following extract. Tripterospermum is described as 
of the same general form as Trigoiiocarpus : ‘ Mais ce testa, tres-tpais, se 
prolonge en trois ailes tres-saillantes, et est compose de deux couches tres- 
distinctes : Pinterne est formee d’un tissu serre, trts-colore et tres-opaque, 
compose de cellules diversement dirigees ; 1’exttrieure, plus large, est 
constitute par un tissu plus lache et plus transparent ’ 7 . One of the 
distinguishing characters here given, viz. the double-layered testa, is now 
known to be shared by Brongniart’s Trigonocarpus pusillus , as shown 
by Prof. Oliver in his recent re-examination of this seed from Grand’- 
Croix 8 . Prof. Oliver shows that the compact layer of the testa is 
1 Oliver (’04) (i). 3 Oliver (’04) (2). 3 Brongniart (’74). 
4 Oliver (’04) (1), p. 389. 5 Hooker and Binney (’55). 6 Williamson (’77). 
7 Brongniart (’74). 8 Oliver (’04) (2), p. 98. 
