166 YATESIA. 



separation between some of the smaller stems of Bucklandia and 

 the yatesian form of trunk. Schimper includes Yatesia Joassiana, 

 Carr., 1 in the genus Clathraria, and expresses surprise that it 

 has been referred by Carruthers to another genus. 



The specimens of Yatesia Morrisii, Carr., described by the 

 author of the species, were obtained from the Lower Greensand 

 beds of Potton and Leighton Buzzard. One of the examples in 

 the National Collection is described as being from the " Wealden" 

 beds of Leighton Buzzard. The exact age of fossils from these 

 beds must be a matter of some uncertainty, owing to the fact 

 of many of them being clearly derived forms ; it may be noted, 

 however, that some of the plant fossils from Potton appear to be 

 specifically identical with Wealden types. 



Among the genera instituted by Saporta, that of Cylindropodium 

 includes some forms of stems which bear a striking resemblance 

 to Carruthers' species of Yatesia. 



Yatesia Morrisii, Carr. 



1867. Gycadeoidea Morrisii, Carruthers, Geol. Mag. vol. iv. p. 199. 



1870. Yatesia Morrisii, Carruthers, Trans. Linn. Soc. vol. xxvi. p. 688, 



pi. Iv. figs. 3-6. 

 1874. Yatesia Morrisii, Schimper, Trait, pal. veg. vol. iii. p. 555. 



Type. Stem with internal structure imperfectly preserved. 

 Royal Agricultural College, Cirencester. 



The following is Carruthers' definition of this species : 

 " Stem cylindrical, covered with the bases of the petioles, which 

 are rhomboidal in form, and terminate in a tumid boss, the apex 

 of which is directed upwards. The cellular axis is very large. 

 The pith has disappeared, except in one specimen, where sufficient 

 of it remains to show that it was permeated with vascular 

 bundles. The woody cylinder surrounding the pith, in the 

 specimen figured, consists of two rings (figs. 5 and 6) ; it is 

 everywhere pierced by medullary rays, which are often so large 

 as to break the continuity of the wood (fig. 6). The sides of the 

 wood-cells parallel to the medullary rays are covered with disks 



1 Schimper, Trait, pal. veg. vol. iii. p. 554. 



