200 CLADOXYLEAE [CH. 



species referred to Eristophyton, but the question as to the degree 

 of affinity to Calamopitys is more difficult to settle. There is 

 force in Zalessky's contention that these two stems should not 

 be retained in Calamopitys : the recently described American 

 species, C. americana Scott and Jeffrey, gives emphasis to the 

 view that the restriction of Calamopitys to the German (and 

 American) types is the safer course. While Calamopitys as thus 

 restricted is almost certainly a Pteridosperm, the inclusion of 

 the types referred to Eristophyton in the same category rests on 

 a more slender basis. 



CLADOXYLEAE. 



This order was founded by Unger 1 for some imperfectly 

 preserved stems from Palaeozoic strata in Thuringia and in it 

 he included the two genera Cladoxylon and Schizoxylon. There 

 is some doubt as to the precise age of the Thuringian beds ; they 

 were assigned by Richter to the Devonian system and subse- 

 quently placed in the Culm : Solms-Laubach in his later reference 

 to Unger's plants favours a Devonian horizon 2 . Unger included 

 the Cladoxyleae in the Lycopodiales, and though this conclusion 

 is not accepted the position of the order is still uncertain. His 

 genus Schizoxylon has no claim to generic separation from Clado- 

 xylon. An inspection of the illustrations in the memoir by Richter 

 and Unger reveals a striking resemblance in the main anatomical 

 features between several types assigned to different genera and 

 distributed among the Cladoxyleae and Rhachiopterideae (a term 

 first used by Corda for petrified rachises or petioles of ferns) and 

 other orders. Solms-Laubach 3 , to whom our more accurate 

 information as to Unger's plants is chiefly due, is inclined to 

 regard the specimens referred by Unger to the genus Arctopodium 

 as young stems of Cladoxylon, and he draws attention to a close 

 similarity between Hierogramma, another of Unger's genera, and 

 Cladoxylon. Paul Bertrand 4 goes further in considering that the 

 following genera represent one generic type, namely Syncardia 

 (fig. 459, F), Hierogramma, Arctopodium, Cladoxylon, and Schizo- 

 xylon. The same author interprets the fossils so named by 



1 Unger and Richter (56) B. p. 178. 2 Scott and Jeffrey (14) p. 364. 



3 Solms-Laubach (96) B. * P. Bertrand (08). 



