OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 515 
extended than is the case in the conjugating cells of the Phycomyces nitens described 
by the French biologists. 
That these dark-coloured, hollow, thin-walled branching tubes are as different as 
possible from the transparent and colourless siliceous spines of the Radiolarians is too 
obvious to require further remark. Soft and flexible in their young state, they became 
brittle only when more matured, a condition to which I have referred in an earlier 
part of this memoir as not uncommon amongst the macrospores of such recent 
Lycopods, as Selaginella Martensii. The cells seen in figs. 42 and 45 are wholly 
undistinguishable from similar endospermic cells seen in the Lycopodiaceous macro¬ 
spores figured in Plate 23 of my last memoir, Part IX. Hence I adhere to my 
previously expressed conviction that the Traquairce are really vegetable organisms, 
and that there are strong grounds for supposing them to be Cryptogamic macrospores. 
Professor Strasburger suggests that their nearest allies will possibly be found in 
those of Azolla and other Rhizocarpous genera. 
In my last memoir I gave small figures (loc. cit., Plate 23, figs. 72, 73, and 74) of 
three small bodies, respecting which I observed : “ It is impossible to overlook the 
striking resemblance of these little objects to the fossil Xanthidia of the chalk flints, 
and to the zygospores of some of the Desmideae.” When these words were penned 
I was not certain that these objects might not prove to be young states of some of the 
numerous spores with which the Halifax rock abounds. Since then I have obtained 
numerous additional examples of these objects in sections for which I am indebted 
to Messrs. Spencer and Earnshaw, and find their characteristic features to be so 
constant that I cannot doubt their being matured organisms, whatever may be their 
botanical nature. That they were all more or less spherical, with radial appendages 
distributed over their entire periphery, is certain. 
Fig. 51 represents one of these objects in their most common aspect. The diameter 
of the central disk is about ’0014. The radiating arms are of somewhat variable 
length. These arms always branch more or less peripherally as represented by the 
further enlarged fig. 52. It is not always easy to trace their exact ramifications owing 
to imperfections in their mineralisation, but in those which are well preserved there 
are usually two or three primary divisions, the extremities of which are further sub¬ 
divided. 
Fig. 53 represents another of these objects, the extreme diameter of the disk of which, 
exclusive of the radiating arms, is ‘0018. The arms in this example are rather shorter 
than in the last one. The section has here passed tangentially through the upper¬ 
most portion of the disk—hence we see at a the bases of arms springing at regular 
intervals from what remains of its convex surface. Fig. 56 is a less highly magnified 
figure of a much larger specimen, the disk of which has a diameter of ’006. It is 
chiefly interesting from the fact that it unmistakably exhibits an inner structureless 
membrane, b, devoid of all radial extensions. I have found faint evidences of the 
existence of such a membrane in several of my specimens, leaving no room for doubting 
