LTCOPODIALES. 67 



to Hquisetites columnaris, but until further evidence of tteir 

 connection is forthooming Bunbury's specific name may be 

 conveniently retained. 



On the same piece of rock there are some good examples of 

 the pinnate fronds of Williamsonia gigas (L. & H.). BecMes Coll. 



V. 2725«(. A fairly common type of cast of this species, in 

 which the nodal regions are marked by distinct constrictions, but 

 without any indication of leaf-sheaths ; 33 cm. in length, 15 cm. 

 broad. The fine longitudinal striations in such casts as V. 2725a, 

 of -which there are several examples in the Museums of Tork, 

 Whitby, and Scarborough, suggest the impression of a cylinder 

 of wood : it has already been pointed out that these larger stems 

 probably possessed the power of secondary thickening. 



Beohles Coll. 



V. 3929, 39,093 [vide Williamsonia gigas (L. & H.)], 40,577. 

 Similar flattened casts, with nodal constrictions and surface striation 

 as in V. 2725«. 



Class LTCOPODIALES. 



Perennial plants of terrestrial, epiphytic, or aquatic habit, 

 usually herbaceous, but more or less shrubby in a few tropical 

 species. Stems for the most part long and slender, dichotomously 

 or monopodially branched; in some forms the stems are short, 

 imbranched, and tuberous. The sporangia are large and exannulate, 

 occurring singly either in the axil of a more or less modified leaf 

 ■or on the lower part of the upper surface of a leaf. 



The living genera iacluded in this class are the isosporous 

 Lyoopodium, Phylloglosmm, Fsilotum, and Tmesipteris, also the 

 heterosporous Selaginella and Isoetes, Isoetes, Selaginella, and 

 Lycopodium are represented by British species, but the other 

 genera have a restricted tropical distribution. The extinct types 

 Lepidodend/ron, Sigillwria, and other Palaeozoic plants belonging 

 "to the Lycopodiaae played an important part in the vegetation of 

 the Carboniferous and Permian periods ; they diSered from the 

 iaodern genera in their arborescent habit and in their power of 

 secondary growth in thickness. 



