IX] PHYLLOTHECA. 281 



Equisetums. The examples which have been selected may 

 serve to illustrate the kind of specimens that are usually met 

 with, as well as some of the possible sources of error which 

 have to be borne in mind in the description of species. 



Such Tertiary species as have been recorded need not be 

 considered ; they furnish us with no facts of particular interest 

 from a morphological point of view. The wide distribution of 

 Equisetites, especially during the Jurassic period, is one of the 

 most interesting lessons to be learnt from a review of the fossil 

 forms. No doubt a detailed comparison of the several species 

 from different parts of the world would lead us to reduce the 

 number of specific names ; and at the same time it would 

 emphasize the apparent identity of fossils which have been 

 described from widely separated latitudes under different names. 



Specimens of Equisetites are occasionally found in plant- 

 bearing beds apart from the other members of a Flora; this 

 isolated manner of occurrence suggests that the plant grew 

 in a different station from that occupied by Cycads and other 

 elements of the vegetation ^ 



A selection of Triassic and Jurassic species arranged in 

 a tabular form demonstrates the world-wide distribution of this 

 persistent type of plant^. 



II. Phyllotheca. 



The generic name Phyllotheca was proposed by Brongniart' 

 in 1828 for some small fossil stems from the Hawkesbury river, 

 near Port Jackson, Australia. The stems of this genus are 

 divided into nodes and internodes and possess leaf-sheaths as 

 in Equisetum, but Phyllotheca differs from other Equisetaceous 

 plants in the form of the leaves and in the character of its 

 sporophylls. We may define the genus as follows: — 



Plants resembling in habit the recent Equisetums. Stems 

 simple or branched, divided into distinct nodes and internodes, 



1 Vide Saporta (73) p. 227. 



2 The distribution will be dealt with in Volume ii. 



3 Brongniart (28) p. 151. 



