760 MR ROBERT KIDSTON ON THE FOSSIL PLANTS OF 



Of these, numbers 2 and 4 are Devonian, the others are carboniferous. 



Ptilophyton Thomsoni must, however, be excluded from the genus, as more perfect 

 specimens show it to belong to a different class of plants from that with which the 

 remaining species of Ptilophyton are supposed to have affinities. The late Sir William 

 Dawson sums up the conclusions to which he had arrived as to the systematic 

 position of Ptilophyton in the following paragraph : — " The species of Ptylophyton will 

 thus constitute a peculiar group of aquatic plants belonging to the Devonian and Lower 

 Carboniferous Periods, and perhaps allied to Lycopods and Pillworts in the organisation 

 and fruit, but specially distinguished by their linear leaves serving as floats, and arranged 

 pinnately on slender stems." * 



The British Museum possesses a fine specimen f from Stonegun, near Thurso, which 

 shows Ptilophyton Thomsoni terminating a stem 16 inches long, and rather less than 

 quarter of an inch thick, and which shows the remains of lateral branches. Similar 

 stems, not showing the terminal portion — the Ptilophyton Thomsoni — cannot be dis- 

 tinguished from stems of Psilophyton, and under the name of Psilophyton Dechenianus, 

 Gopp., sp., I have recorded these, j believing that plant to be synonymous with 

 Psilophyton robustius, Dawson, but I now regard these two plants as specifically 

 distinct. 



From the further study of additional material within the last few years, I have now 

 little doubt that the stem described as Caulopttris (?) Peachii by Salter § is only the 

 larger trunk which bore the branches I identified as Psilophyton Dechenianus, and 

 whose terminal portion, as already stated, is the Ptilophyton Thomsoni of Dawson. It 

 is impossible, therefore, to include Ptilophyton Thomsoni in the genus Ptilophyton as 

 defined by Dawson. 



The Ptilophyton lineare, Lesq., sp., I would also feel inclined to exclude from 

 Dawson's genus, but not having seen any specimens of this plant it is unsafe to 

 express any definite opinion on this point. 



Dawson and Lesquereux had apparently no doubt as to the vegetable nature of 

 Ptilophyton, but their figures do not show all the characters they mention ; and 

 judging from the only examples of Ptilophyton which have come under my 

 observation, and which are certainly the Ptilophyton plumula, Dawson, I must 

 confess to still having some doubt as to the vegetable nature of the organisms included 

 in this genus. 



Hall || at one time described the fossils subsequently placed in Ptilophyton by 

 Dawson under the name of Ptilophyton Vanuxemi as perhaps crinoid tentacles, or 

 more probably analogous to the Sertularia, and regarded them as animal structures. 



* " Fossil Plants, Erian (Devon.) and Upper Silur. Forms, of Canada," part ii. p. 122, 1882. 



t Geol. Department, Registration No. V1419. 



X Catal. of Palceozoic Plants in the British Museum, p. 232. 



§ Caulopteris (?) Peachii, Salter, Quart. Journ. Geol. Soc, vol. xv. p. 408, fig. 14. 



|| Vanuxem, Nat. Hist. New York, " Geol. of New York," part iii., Survey of the Third Geological District, p. 175, 

 fig. 46, 1842 ; also Hall, Nat. Hist, of New York, "Geol. of New York," part iv., Geol. of Fourth Geol. District, p. 273, 

 fig. 125, Albany, 1843. 





