The Present Position of Palaeozoic Botany. 143 



question. The fossil known as Girvanella, consisting of minute inter- 

 woven tubular filaments, has been identified in Silurian, Ordovician, 

 and even Cambrian rocks; its systematic position, however, is unde- 

 termined and it has been referred to families as remote from each, 

 other as the Cyanophyceae and the Siphoneae. It is of interest to 

 find that there is good evidence for the existence of the non-cellular 

 group Siphoneae in early Palaeozoic times. The calcified verticillate 

 forms are favourable for preservation and specimens referable to this 

 type have been found in rocks as old as the Silurian and Ordovician 

 {ArtJiroporeUa, Sycidimn, Cydocrimis, etc.). 



The most remarkable of all fossil Algae, Nematophycus, has been 

 variously referred to the Siphoneae and the Phaeophyceae, A species 

 of this genus, the gigantic N. Logmii, was first discovered by D a w s o n 

 in 1856, in the Lower and Middle Devonian of Canada. It was 

 originally described as a Conifer and named Prototaxites, but C-arru- 

 thers in 1872 proved it to be an Alga, and gave it its present generic 

 name. In Nematophycus Logani the stem, which is silicifled, may be 

 almost a metre in diameter. The tissue consists of large, non-septate 

 hyphae, among which smaller, occasionally septate tubes are inter- 

 woven. Concentric rings of growth are present, as in recent Lami- 

 narieae, and radiating gaps in the tissues have been compared to 

 the air-spaces of the larger Algae, In other species, such as 

 N. Storriei, Barber, from the Silurian of South Wales, and N. Ortoni, 

 Penhallow, from the Devonian of Canada, there is somewhat less 

 differentiation of the tissues. In the latter, however, the tubes, 

 dilated at intervals, have been compared with the trumpet-hyphae of 

 Laminaria. On the whole the evidence cannot be regarded as decisive 

 either for Siphoneous or Phaeophycean affinities. Pachytheca, a small 

 spherical organism somewhat resembling Nematophycus in histological 

 structure, has been found at similar horizons, but there are no good 

 grounds for assuming a connection between the two. 



A carbonaceous material, known as boghead coal or torbanite, 

 occurring in Carboniferous rocks in Scotland, France and New South 

 Wales, has been found by Eenault and Bertrand to consist 

 mainly of countless multitudes of organisms, interpreted as gelatinous 

 Algae. The th alius is a minute, spherical {Pila) or lobed {Reinschia) 

 body, consisting of a single layer of cells enclosing a central cavity. 

 The specimes are well preserved , and there seem to be good 

 grounds for the authors' interpretation. The material is rich in 

 bitumefl, which appears to have replaced the water which presu- 

 mably must once have formed a large constituent of such gelatinous 

 organisms. 



There is no conclusive evidence for the existence of Palaeozoic 

 Florideae, but Soïenopora, which goes back to the Ordovician, has 



