130 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



" Sur la valeur du genre Trizygia" to the Soc. Geol. de France, 

 in which he advocates the union of Trizygia and Sphenophyllum. 

 He cites several cases where well-known species of Sphenophyllum 

 have been known to show an inequality in the size of the leaves 

 forming the whorl, and simulating in this respect the charac- 

 teristics of Trizygia. 2 



It must be noted, however, that in Trizygia the inequality in 

 the size of the leaves in the whorl is a constant character, but in 

 Sphenophyllum it is an accidental occurrence. 



Seward in his Fossil Plants unites these two genera, 3 but 

 this course I do not feel inclined to adopt, and prefer to leave 

 the question open for the present. 



Sphenophyllum, not only in the structure of its stem, but also 

 in that of its cones, exhibits so many peculiarities that it is im- 

 possible to class it with any other group of plants. With the 

 Catamites it has a certain superficial resemblance in the ribbed 

 stem and whorled leaves, but the solid axis, the non-alternating 

 ribs of Sphenophyllum, its dichotomous division of the segments 

 and veins of the leaves, and also the structure of its cone, differ 

 so much from those of the Calamites that any systematic re- 

 lationship is entirely precluded. With Archceocalamites (Bornia) 

 it has a greater resemblance in the ribs of Archceocalamites not 

 alternating at the nodes and in the leaves being dichotomously 

 divided, but it differs here also in its solid axis 4 and in the 

 structure of the cone (presuming that Pothocites is the fructifica- 

 tion of Archceocalamites). b 



With the Lycopodiacece also, Sphenophyllum seems to have no 

 close connection. When describing the fructification of Spheno- 

 phyllum trichomatosum, Stur, in 1891, my belief was that 



1 Bull., 3* Sir., Vol. XIX., p. 673. 1891. 



2 For reference to these figures, see Zeiller's paper, I.e. 

 3 Seward, Fossil Plants, Vol. I., p. 411. 



4 For structure of Archceocalamites Gopperti, see Solms-Laubach, Uber 

 die in den Kalksteinen des culm von Glatzisch Falkenberg in Schlesien 

 erhaltenen structur Jnetenden Pjlanzenreste. Botanisches Zeitung, 1S97, 

 Heft. XII., p. 219, PI. VII. 



5 Kidston, " On the Affinities of the genus Pothocites," Paterson. Ann. 

 and Mag. Nat. Hist., Ser. 5, Vol. XL, p. 297, Pis. IX., X., XI., figs. 9-10; 

 XII., figs. 13-16, 1883; ibid., Proc. Roy. Phys. Soc. Edin., Vol. XVI., 

 Pis. L, II, III., figs. 9-10; IV, figs. 13-17 



