190 CALAMOPITYEAE [CH. 



Ptychoxylon differs considerably from Medullosa, which Renault 

 included in the Cycadoxyleae, in the plan of the vascular 

 system: there is nothing corresponding to the 'partial pith' or 

 primary region which forms the central portion of the plate- 

 and snake-rings in Medullosa. The double leaf-trace and the 

 absence of the Medullosa type of hypoderm are other dis- 

 tinguishing features. The paired leaf-bundles suggest comparison 

 with Lyginopteris among other genera and, as Scott 1 points out, 

 the internal arcs of inversely orientated tissue which sometimes 

 occur in the peripheral region of the pith of Lyginopteris 

 (fig. 405, C, c) behave like the internal bands of Ptychoxylon in 

 occasionally joining the main cylinder at a leaf -gap ; but the 

 differences outweigh the resemblances. As regards the general 

 arrangement of the vascular tissue in two irregular concentric 

 circles and their connexions with one another, but not in the 

 structure of the xylem and phloem, there is a similarity between 

 this genus and such a Fern as Matonia. In the varying patterns 

 formed by the vascular system at different levels in the stem 

 Ptychoxylon resembles the Ferns Polypodium quercifolium and 

 P. heracleum 2 . 



CALAMOPITYEAE. 



Calamopitys. linger. 



In 1856 Unger 3 described several fragmentary petrifactions 

 from Thuringian strata of Upper Devonian age, the majority of 

 which he referred to the Calamarieae and the Rhachiopterideae. 

 In an earlier publication 4 he gave a list of species including two 

 families/ the Haplocalameae and the Calamoxyleae, assigned by 

 him to the group Calamarieae : in the Haplocalameae he placed 

 the new genera Kalymma, Calamosyrix, Calamopteris, and Haplo- 

 calamus. These were subsequently examined by Graf Solms- 

 Laubach and identified as portions of petioles, for the most part 

 belonging to unknown stems. In his second family, the Calamo- 

 xyleae, Unger included the single genus Calamopitys represented 

 by the type-species C. Saturni. The type-specimens have been 

 thoroughly investigated by Solms-Laubach 5 who instituted the 



1 Scott (09) B. p. 492. 2 Klein (81). 



3 Richter and Unger (56) B. 4 Unger (54) p. 599. 



5 Solms-Laubach (96) B. 



