282 PTERIDOPHYTA. [CH. 



the latter marked by longitudinal ridges and grooves ; from the 

 nodes are given off leaf-sheaths consisting of linear-lanceolate 

 uninerved segments coherent basally, but having the form of 

 free narrow teeth for the greater part of their length. The 

 long free teeth are usually spread out in the form of a cup and 

 not adpressed to the stem, the tips of the teeth are often in- 

 curved. 



The sporangia are borne on peltate sporangiophores attached 

 to the stem between whorls of sterile leaves. 



Our knowledge of Phyllotheca is unfortunately far from 

 complete. The chief characteristic of the vegetative shoots 

 consists in the cup-like leaf-sheaths ; these are divided up into 

 several linear segments, which differ from the teeth of an 

 Equisetum leaf-sheath in their greater length and in their 

 more open and spreading habit of growth. The large loose 

 sheaths of the fertile shoots of some recent Horse-tails bear 

 a certain resemblance to the sheaths of Phyllotheca. The 

 diagnosis of the fertile shoots is founded principally on some 

 Permian specimens of the genus described by Schmalhausen 

 from Russia^ and redescribed more recently by Solms-Laubach^ 

 Prof. Zeiller^ has, however, lately received some examples of 

 Phyllotheca from the Coal-Measures of Asia Minor which bear 

 strobili like those of the genus Annularia, a type which is dealt 

 with in the succeeding chapter. A description of a few species 

 will serve to illustrate the features usually associated with this 

 generic type, as well as to emphasize the unsatisfactory state of 

 our knowledge as to the real significance of such supposed 

 generic characteristics. 



There are a few fossil stems from Permian rocks of 

 Siberia, from Jurassic strata in Italy, and from Lower Mesozoic 

 and Permo-Carboniferous beds in South America, South Africa, 

 India and Australia which do not conform in all points to the 

 usually accepted definition of Equisetites, and so justify their 

 inclusion in an allied genus. On the other hand there are 

 numerous instances of stems or branches which have been 



1 Schmalhausen (79) p. 12, PI. i. figs. 1—3. 



2 Solms-Laiibach (91) p. 181. ^ Zeiller (96), 



