546 MR ROBERT KIDSTON ON 



1883. Williamson. " On the Organisation of the Fossil Plants of the Coal Measures," 



Part XII., Phil. Trans., p. 466. 



The chief point of interest in this communication in regard to the subject under 

 discussion, is the figure of the specimen of Halonia in the Leeds Museum, of which a 

 figure had previously been given by Mr Denny.'" Professor Williamson referring to 

 this specimen says — " It is yet more perfect than Mr Carruthers' specimen,! since its 

 lower extremity exhibits much more markedly than his corresponding ones do, the 



elongated foliar cicatrices characteristic of Lepidodendron." "At the lower 



part of the branch (A on Professor Williamson's plate xxxiv.) these leaf-scars have 

 exactly the same form as those of L. selaginoides and L. elegans of Lindley and Hutton." 

 " After its first bifurcation, the two branches still contain much of the Lepidodendroid 

 features, though the leaf-scars gradually become less elongated vertically." After further 

 description of this specimen in the Museum of the Leeds Phil. Soc, he sums up as 

 follows — " In my second Memoir (Phil. Trans., 1872, p. 222), read in June 1871, I said, 

 ' I have little doubt but that Halonia belongs to the upper branches of a Lepidodendroid 

 tree, consequently it cannot be a root ;' secondly, we learn that Halonia is a specialised 

 branch of a Lepidodendroid tree that is not itself a Halonia." These conclusions are 

 very similar to those arrived at by Mr Carruthers in 1873 (loc. cit.), where, in speaking 

 of one of the specimens he described, he says — "With Bergeria must go Halonia as a 

 separate genus, seeing that it is only a condition of Lepidophloios and it may be of other 

 Lepidodendroid plants." " The specimen now described is unquestionably not a Loma- 

 tophloios but a true Lepidodendron." I am sorry I must entirely dissent from the inter- 

 pretation of the affinities of the two specimens described and figured by Professor 

 Williamson (loc. cit, pi. xxxiv.) and Mr Carruthers (loc. cit., pi. vii. fig. 1). 



Firstly, in regard to that figured and described by Professor Williamson. This 

 specimen I most carefully examined in 1886, while studying the fossil plants in the 

 Museum of the Leeds Phil. Soc, and it is correctly described by Denny as " apparently 

 combining the characters of the genera Halonia and Knorria" (loc. cit., p. 37). 



Now Knorria may arise from Lepidophloios, Lepidodendron, and Bothrodendron, 

 or even the Clathrate Sigillarice ; it is only a condition of imperfect preservation — a state 

 in which the outer surface of the stem has been removed, and hence such specimens as 

 that described by Denny, and more lately by Professor Williamson, do not and cannot 

 possess the characters necessary for a generic determination. Professor Williamson has 

 himself pointed out that Halonia is a semi-decorticated condition (ante, p. 545). Hence 

 this specimen, on which Professor Williamson places so much importance, proves 

 absolutely nothing, either for or against his opinion on the relationship of Halonia to 

 Lepidodendron. The relationship of Halonia to its parent stem can only be determined 

 from specimens, on which is preserved, not only the Halonia tubercle, but the form and 



* See I. c. ante, p. 532. 



+ This specimen is refigured on my PI. II. fig. 8. It is a Lepidophloios, not a Lepidodendron. 



