Johnson — On Bothrodendron {Cychstigma) kiltorkense. 523 



B. kiltorkense type of Club-moss was prevalent in the Devonian and to a less 

 extent in the Lower Carboniferous epochs wherever there was a land habitat 

 suitable for it in the world. 



Systematic Position of Bothrodendron. 



The Bothrodendracese have been regarded as a small group, intermediate 

 between the Lepidodendracese and the Sigillariacese, while F. E. Weiss placed 

 Bothrodendron under Sigillaria as a subgenus. Kidston, the latest writer on 

 Bothrodendron, sees features in it found partly in Lepidodendron and partly 

 in Sigillaria. He regards it in consequence as a connecting link between 

 these two genera, with additional characters of its own. 



The records of the rocks show that Bothrodendron is at its maximum 

 development in the Devonian epoch, Lepidodendron in the Lower Coal 

 Measures, Sigillaria in the Middle Coal Measures. In the Pre-Culmian beds, 

 yielding Bothrodendron in Ireland, and in the Harz Mountains and else- 

 where, Lepidodendron is either absent or sparingly represented. McLean 

 also concludes from the examination of the prothallus of B. mundum that 

 Bothrodendron is more primitive than Lepidodendron. The general 

 evidence seems to me to favour the view that Bothrodendron is an 

 earlier type than Lepidodendron, which, with Sigillaria, are types derivable 

 from Bothrodendron, i.e., that Bothrodendron, though heterosporous, is the 

 earliest and most primitive of the Lepidophytes. The young shoots of 

 Bothrodendron are so much like those of Lepidodendron that records based 

 on them, unsupported by stem-impressions showing typical leaf-cushions, 

 are unreliable. 



Summary. 



In Bothrodendron kiltorkense the stem attained a length of 8 metres and 

 a breadth of 30 centimetres or more (24 feet long and 1 foot broad). 

 It branched frequently and dichotomously, and carried leaves which formed 

 apical tufts. The leaf was long, linear-subulate, and early deciduous. A 

 single median bundle runs the whole length of each leaf. The leaves are 

 clearly arranged in whorls at first, but become distant and quincuneially 

 arranged in older stems, owing to unequal extension of the stem surface. 

 The leaf-scars are always small, and, papillate at first, become flush with the 

 stem surface later on, or even a little sunk below it. Sometimes, however, 

 the papillae are quite pronounced in older stems. The leaf-scar, in a 

 well-preserved stem, shows the usual lepidophyte sears, specks, or cicatrieules, 

 but the ligular scar is difficult, often impossible, to observe with certainty. 

 The shape of the leaf-scar changes with age. In the young shoot it is 

 circular-triangular, with the apex directed upwards, and in older shoots sub- 



SCIENT. PKOC. K.D.S., VOL. XHI., NO. XXXIV. 4 H 



