XXXVni] COLYMBETES 491 



this name by Schenk from the Wealden of North Germany. 

 From Liassic beds in Normandy Lignier figures two species of 

 Cycadeomyelon, C. Apperti and C. densecristatum. The surface- 

 features of Cycadeomyelon resemble those of the Palaeozoic genus 

 Tylodendron (see "Vol. iv.), but in the latter genus the nodal 

 swellings are a characteristic pecuUarity. Though medullary 

 casts of this type are of no great botanical importance and their 

 specific distinctions are of little value, it is safe to assume that 

 broad medullary casts with comparatively large lozenge-shaped 

 areas belong to Cycadean stems, while narrower specimens with 

 smaller lozenges are more likely to be pith-casts of Coniferous 

 stems. 



Lester Ward^ instituted the genus Feistmantelia for some 

 Lower Cretaceous casts from the Black Hills which he compared 

 with an Indian fossil from Cutch described by Feistmantel as 

 'the stem of a Coniferous plant^,' and with pith-casts figured 

 by Stokes and Webb as Clathraria cmomala. It is impossible to 

 determine the systematic position of such imperfect specimens 

 as that on which Ward founded his species F. ohlonga : they may, 

 as Hollick and Jeffrey* suggest, be casts of the bark of some 

 Conifer; there is certainly no good reason for connecting them 

 with Cycads. 



COLYMBETES. Stopes. 



Colymbetes Edwardsi Stopes. This genus* is founded on the 

 inner portion of a petrifi.ed trunk which was probably cylindrical 

 and more than 12 cm. in diameter, consisting of a pith,. 7-5 cm. 

 in diameter, and part of a vascular cylinder of remarkable structure. 

 The type-specimen is of Aptian age and may have come from 

 Leighton Buzzard (Bedfordshire). The pith (fig. 580, p) consists 

 of large parenchymatous cells and numerous secretory canals: 

 the perimeduUary zone, pm, is characterised by the occurrence 

 of loosely disposed tracheids in groups and radial rows pursuing 

 a sinuous longitudinal course in the accompanying parenchyma. 

 The tracheids in this region are small in diameter and have oval, 

 scalariform, or circular pits. Abutting on the perimeduUary 



' Ward (99) B. p. 693, PI. 169, fig. 19. 



2 Feistmantel (76^) PI. x. fig. 2. ' Hollick and Jeffrey (09) B. p. 17. 



* Stopes (15) p. 314, Pis. xxxi., xxxn., text-figs. 101 — 111. 



