732 FOSSIL PLANTS OF THE CAEBONIFEROUS SYSTEM. 



to the rachis, sometimes confluent, a strong primary vein reaching the 

 apex, the secondary veins being nearly straight, simple, or forked, 

 rarely pinnate, sori rounded at the end of the secondary veins (fig. 

 909). In Neuropteris {mu^ov, a nerve) the frond is pinnate or bi- 

 pinnate, pinnse sub-cordate at the base, distinct from the rachis, 

 strong primary vein vanishing towards the apex, secondary veins 

 oblique, arched, repeatedly diohotomous (fig. 910). Lonchopteris has 

 its frond multi-pinnatifid, and the leaflets more or less united together 

 at Ithe base ; midrib is distinct, and the veins are reticulated. 

 Cyclopteris has simple orbicular leaves, undivided or lobed at the 

 margin, the veins radiating from the base, with no midrib. Schizo- 

 pteris resembles the last, but the frond is deeply divided into numerous 

 unequal segments, which are usually lobed and taper-pointed. Oaulo- 

 pteris and Psaronius are names given to the stems of Tree-ferns found 

 in the coal-fields. Tree-ferns appear to have existed in Britain during 

 the deposit of the coal strata, and to have occupied an important 

 place in the flora. The stems of these ferns are included under the 

 genus Caulopteris. The fronds have not been found attached ; but it 

 is probable that some of the fronds found in the Coal-measures have 

 been connected with these stems. Prof W. C. Williamson says that 

 the number of fossil ferns has been needlessly multiplied, and he 

 includes the entire series of four petioles and stems found in the Coal- 

 measures under the name Rachiopteris. These petioles belong, no 

 doubt, to the difierent forms of fronds already described, such as 



Fig. 912. 



Pecopteris, Sphenopteris, etc. The way in which the vascular bundles 

 in the four stems are arranged, are, he says, represented by the letters 

 H, T, V, and X. As a general rule the secondary bundles are given 



Mg. 911. Lepidodendron crenatum, witli the scars of tlie leaves on its stem. It belongs 

 to a family of plants apparently intermediate between Coniferse and LyeopodiaceEe. Fig. 

 912, Lepidodendron elegans, with its dichotomous trunk and linear acute leaves. 



