X] ARCHAEOCALAMITES. 387 



the usual type of Calamitean leaf. The specimens described 

 by Schiraper are in the Strassburg Museum ; the leaf-sheath 

 which he figures is not very accurately represented. 



The example given in fig. 103 shews very clearly the con- 

 tinuous course of the ribs and grooves of the pith-cast. Each 

 rib is traversed by a narrow median groove which would seem to 

 represent the projecting edge of some hard tissue in the middle 

 of each principal medullary ray of the stem. The specimen was 

 found in a Carboniferous limestone quarry, Northumberland; 

 there is a similar cast from the same locality in the Museum of 

 the Geological Survey. 



Affinities of Archaeocalamites. 



This genus agrees very closely with Calamites both in the 

 anatomical structure of the stem and in the verticillate disposi- 

 tion of the leaves. The strobili appear to be Equisetaceous in 

 character, and there is no satisfactory evidence of the existence 

 of whorls of sterile bracts in the cone, such as occur in 

 Calamostachys and in other Calamitean strobili. The continuous 

 course of the vascular bundles of the stem from one internode 

 to the next is the most striking feature in the ordinary specimens 

 of the genus ; but it sometimes happens that the grooves on a 

 pith-cast shew the same alternation at the node as in Calamites. 

 This is the case in a specimen in the Goppert collection in 

 the Breslau Museum, and Feistmanter has called attention to 

 such an alternation in specimens from Rothwaltersdorf In the 

 true Calamites, on the other hand, the usual nodal alternation 

 of the vascular strands is by no means a constant character'^. 

 Stur^ Rothpletz^ and other authors have pointed out the re- 

 semblance of Archaeocalamites to Sphenophyllum. The deeply 

 divided leaves of some Sphenophyllums and those of Archaeo- 

 calamites are very similar in form ; and the course of the 

 vascular strands in Sphenophyllum may be compared with that 

 in Archaeocalamites. But the striking difference in the structure 



' Feistmantel (73), p. 491, PI. xxiv. figs. 3 and 4. 



'■^ Vide specimens 20 A, 20 B, 24 in the Williamson Collection. 



3 Stur (76), p. 17. •* liothpleta (80), p. 8. 



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