290 PTERIDOPHYTA. [CH. 



Calamiteaa plants. An Equisetaceous species has been described 

 from the Newcastle Coal-Measures of Australia by Etheridge^ 

 in which there are two forms of leaves, some of which closely 

 resemble those of Phyllotheca indica, while others are compared 

 with the sterile bracts of Gingularia, a Calamitean genus 

 instituted by Weiss'. 



When we turn to other recorded forms of Phyllotheca many 

 of them appear on examination to have been placed in this 

 genus on unsatisfactory grounds. Heer figures several stem 

 fragments from the Jurassic rocks of Siberia as P. Sibirica 

 Heer^ and it was the resemblance between this form and the 

 English Equisetites lateralis which led to the substitution of 

 Phyllotheca for Equisetites in the latter species. Without 

 examining Heer's material it is impossible to criticise his 

 conclusions with any completeness, but several of his specimens 

 appear to possess leaf-sheaths more like those of Equisetum than 

 of Phyllotheca. 



The frequent occurrence of isolated diaphragms and the 

 comparatively long acuminate teeth of the leaf-sheath afford 

 obvious points of resemblance to Equisetites lateralis. Some 

 of the examples figured by Heer appear to be stem fragments, 

 with numerous long and narrow filiform leaves different in 

 appearance from those of other specimens which he figures. 

 It may be that some of the less distinct pieces of stems are 

 badly torn specimens in which the internodes have been 

 divided into filiform threads. Heer also figures a fertile axis 

 associated with the sterile stems, and this does not, as Heer 

 admits, show the alternating sterile bracts such as Schmalhausen 

 has described. So far as it is possible to judge from an exami- 

 nation of Heer's figures and a few specimens from Siberia in 

 the British Museum — and this is by no means a safe basis on 

 which to found definite opinions — there appears to be little 

 evidence in favour of separating the fossils described as Phyl- 

 lotheca Sibirica from Equisetites. This Siberian form may 

 indeed be specifically identical with Equisetites lateralis Phill. 



Various species of Phyllotheca have been described from 



1 Etheridge (95). 2 Weiss (76) p. 88. 



3 Heer (77) p. 43, PI. iv. (78) p. 4, PI. i. 



