OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
253 
beautiful seed represented in figs. 115 a & 115 b. It is the only example I have seen 
from the Oldham nodules resembling M. Brongniart’s genus Hexapterospermum. Spe- 
cimen fig. 115 a represents a side view of the seed of its natural size; and fig. 115 b 
exhibits the same seed enlarged 3 diameters. It differs primarily from Trigonocarpon in 
having six projecting angles instead of three. These ridges, which are very sharply defined, 
also terminate in a ring of prominent protuberances at the base of the seed, instead of 
gradually disappearing on approaching the chalaza. Lindley and Hutton described a 
six-angled seed under the name of Trigonocarpon Noggerathii, which they only distin- 
guish from T. olivceforme in being more oblong and in having six angles instead of 
three. I think there can be no doubt that fig. 115 represents a young form of the same 
seed. I found in the Museum of the Yorkshire Philosophical Society a sandstone 
cast of a similar seed from Aldwark, near Rotherham, but it was fully 1^ inch in 
length. According to M. Brongniart’s description, the internal structure of his Hexa- 
pterospermum stenopterum is almost identical with that of our Trigonocarpon olivce- 
forme, which plant he separates from the genus Trigonocarpon under the name of 
Tripterospermum. This division into three genera of plants which resemble each other 
so closely, both in their internal organization and in their general external form, is 
extremely objectionable. The incidental circumstance that one seed dehisced into 
three segments and another into six, is surely insufficient ground for more than a specific 
distinction. In like manner he distinguishes his allied genus Ptychotesta by a character 
which my transverse sections unequivocally show to exist equally in Trigonocarpon 
olivceforme. He says “ les six ailes qui prolongent les angles de la graine a section 
hexagonale sont en effet formees, non par une extension du tissu du testa, mais par le 
testa lui-meme replie a l’exterieur. Ces ailes ont ainsi une double paroi identique, 
pour sa structure et son epaisseur, au testa qui entoure le corps de la graine.” Surely 
this is substantially what we do see in my figure 104 and other sections. All these 
genera will require to be corrected unless other distinctive characters be found 
presenting better reasons than we now possess for keeping them separate. 
There is great confusion in the nomenclature of these Trigonocarpoid seeds, arising 
from our inability to determine how far size constitutes a legitimate specific distinction. 
At Peel Quarry I find considerable variation in the dimensions of what are unmistakable 
examples of T. olivceforme. Excepting in size, I discover no difference between the 
largest of these specimens and the T. ovatum and T. oblongum of Bindley and Hutton’s 
‘ Fossil Flora.’ Professor Newberry evidently recognizes this fact, since the two 
examples of Hildreth’s Trigonocarpon triloculare which he has figured ( loc . cit. pi. 42. 
figs. 1-13, 13 a) differ in size quite as much as do the T. olivceforme and T. ovatum of 
the 4 Fossil Flora.’ At the same time I cannot see any difference between the latter 
species and that described by Hildreth. I have already referred to the similar differ- 
ence in size between Mr. Aitken’s specimen of Hexap terospermum and that in the 
York Museum. The T. Dawesii (‘ Fossil Flora,’ pi. 221), of which I have specimens 
from Peel Quarry, appears to me to be distinct. In addition to its large size (2J inches 
MDCCCLXXVII. 2 N 
