IX] PALAEOZOIC EQUISETITES. 261 



while poiating out that this distinction does not possess much 

 value as a generic character, retains the genus Equisetites for 

 certain Palaeozoic Equisetum-like leaf-sheaths. 



Fig. 56 represents a rather faint impression of a leaf-sheath 

 and nodal diaphragm. The specimen is from the Coal-Measures 

 of Ardwick, Manchester. The letter a probably points to the 

 attachment of the sheath to the node of the stem. The flattened 

 sheath is indistinctly divided into segments, and at the middle 

 of the free margin there appears to be a single free tooth. The 

 lower part of the specimen, as seen in the figure, shows the 

 position of the nodal diaphragm. Between the diaphragm and 

 the sheath there are several slight ridges converging towards 

 the nodal line ; these agree with the characteristic ridges and 

 grooves of Calamite casts which are described in detail in 

 Chapter X. There is another specimen in the British 

 Museum which illustrates, rather more clearly than that shown 

 in fig. 56, the association of a fused leaf-sheath with a type of 

 cast usually regarded as belonging to a Calamitean stem. 

 Some leaf-sheaths of Permian age described by Zeiller^ as 

 Equisetites Vaujolyi bear a close resemblance to the sheath in 

 fig. 58 E. The nature of the true Calamite leaves is considered 

 more fully on a later page. 



The examples of supposed Equisetites sheaths referred to 

 below may serve to illustrate the kind of evidence on which 

 this genus has been recorded from Upper Palaeozoic rocks. I 

 have retained the name Equisetites in the description of the 

 species, but it would probably be better to speak of such 

 specimens as ' Calamitean leaf-sheaths ' rather than to describe 

 them as definite species of Equisetites. We have not as yet any 

 thoroughly satisfactory evidence that the Equisetites of Triassic 

 and post-Triassic times existed in the vegetation of earlier 

 periods. 



In Grand'Eury's Flore du Oard'' a fossil strobilus is figured 

 under the name Galamostachys tenuissima Grand'Eury, which 

 consists of a slender axis bearing series of sporophylls and 



1 Zeiller (92=) p. 56, PI. xii. Other Bimilar leaf-sheaths have been figured by 

 Germar (U) PI. x. , Schimper (74) PI. xvii. and others. 

 ■^ Grand'Eury (90) p. 223, PI. xv. fig. 16. 



