548 MR ROBERT KIDSTON ON 



if it is necessary to define a difference between the Ulodendron condition and the 

 Halonia condition, even in the absence of the bark they can be separated, the former 

 having two vertical rows of alternate (usually) cup-shaped scars, and the former having 

 more than two rows of (usually) conical tubercles, spirally arranged. 



I perfectly agree in the conclusion to which Professor Williamson arrived, and have 

 always contested for the same issue, viz., " These two names, Halonia and Ulodendron, 

 have no longer any value, but the terms Halonial and Ulodendroid may be conveniently 

 retained as adjectives applicable to appropriate specific forms." These terms are convenient 

 for distinguishing a condition, though the Halonial condition is always referable to the 

 genus Lepidophloios and to that genus alone, while the Ulodendron condition may belong 

 to Bothrodendron* Sigillaria, or Lepidodendron, and when the leaf-scars are not 

 preserved in such a state as to admit of a generic identification, the term " Ulodendroid 

 condition " is of distinct value. 



In the same communication, Professor Williamson refers to the structure of the three- 

 leaf cicatricules, and for the two lateral, which are not connected with the vascular system, 

 but which are probably glandular, adopts the name of parichnos, which has been applied 

 to them by M. HovELACQUE.t The central cicatricule only belongs to the vascular system. 

 Professor Wiliamson rejects the term " ligule "-scar, first applied by Stur to the cicatrice 

 on the leaf-cushion immediately above the leaf-scar, " on the ground that he cannot 

 identify the fossil structure with the organ bearing the same name in Isoetes and 

 Selaginella," a conclusion with which I concur. 



I have not made any remarks on the internal structure of Lepidophloios, as I have 

 nothing to add to that given by Dawes, Binney, and Williamson, in their Memoirs. 



I would only remark that the internal structure of Lepidophloios is of the same type 

 as Lepidodendron, and unless the stems show the Halonial tubercles or leaf-scars, they 

 cannot be distinguished from Lepidodendron, which is seen from the circumstance that the 

 plant originally described by Professor Williamson as Lepidodendron fuliginosum, has been 

 proved by the occurrence of a specimen showing the leaf-scars to be a Lepidophloios. 

 Of course there are specific differences in the structure of the stem, but nothing 

 amounting to what could be regarded as of generic importance, and this is quite what 

 might be expected in two genera which hold such close affinity to each other. 



From what has now been stated, it is seen that some writers regard Lepidophloios, 

 Lomatophloios, and Halonia as distinct genera. Cyclocladia, Goldenberg (not L. and H.), 

 has been accepted generally as synonymous with Halonia. Others unite Lepidophloios 

 and Lomatophloios, while they keep Halonia separate, and some have united all these 

 genera under Lepidophloios. 



It has also been proposed to unite Halonia with Lepidodendron. 



It has, further, been supposed by some that the leaf-scars in all species of Lepi- 

 dophloios were situated at the lower end of the cushion ; by others, that they occupied 



* In Bothrodendron, the umbilicus is eccentric, in the others, it is almost or quite central, 

 t Comptes rendus, vol. cxiii., 13th July 1891 ; also ibid., 15th Aug. 1891. 



