IX] EQUISETITES LATERALIS. 277 



the stems, and to one of them is attached a portion of a 

 leaf-sheath. Solms-Laubach^ points out that the internodal 

 position of these supposed scars is an obvious difficulty; we 

 should not expect to find branches arising from an internode. 

 After referring to some specimens in the Oxford museum, he 

 adds — " In presence of these facts the usual explanation of these 

 structures appears to me, as to Heer, very doubtful.... We are 

 driven to the very arbitrary assumption that they represent the 

 lowest nodes of the lateral branches which were inserted above 

 the line of the nodes of the stem." Circular discs similar to 

 those of E. lateralis have been found in the Jurassic rocks of 

 Siberia^ and elsewhere. There are one or two examples of 

 such discs from Siberia in the British Museum. If the nodal 

 diaphragms were fairly hard and stout, it is easy to conceive 

 that they might have been pressed out of their original position 

 when the stems were flattened in the process of fossilisation. It 

 is not quite clear what the radial spoke-like lines of the discs 

 are due to ; possibly they mark the position of bands of more 

 resistant tissue or of outgoing strands of vascular bundles. 

 A detached diaphragm is seen in fig. 64 C ; in the centre it 

 consists of a flat plate of tissue, and the peripheral region is 

 traversed by the radiating lines. In the stem of fig. 64, A 

 the deeply divided leaf-sheaths are clearly seen, and an im- 

 perfect impression of a diaphragm is preserved on the face of 

 the middle internode. In fig. 64 B a flattened leaf-sheath is 

 shown with the free acuminate teeth fused basally into a 

 continuous collar^. The short piece of stem of Equisetites 

 lateralis shown in fig. 58, F, shows how the free teeth may be 

 outspread in a manner which bears some resemblance to the 

 leaves of Phyllotheca, but a comparison , with the specimens 

 already described, and a careful examination of this specimen 

 itself, demonstrate the generic identity of the species with 

 Equisetites. The carbonaceous film on the surface of such 

 stems as those of fig. 58, F, and 64, A, shows a characteristic 

 shagreen texture which may possibly be due to the presence of 

 silica in the epidermis as in recent Horse-tails. 



1 Solms-Laubaoh (91) p. 180. ^ c/. p. 283. 



3 There is a similar speoimen in the Oxford Museum. 



