126 BUCKLANDIA. 



originally occupied by the cells of the primary medullary rays. 

 In speaking of the numerous specimens of these pith casts, 

 Carruthers admits the impossibility of referring them with any 

 certainty to their respective species of bucklandian stems, and 

 suggests that probably they may belong to three or four distinct 

 forms of the genus. Saporta l has instituted a comprehensive 

 genus, Cycadeomyelon, with the following definition: "Medulla 

 centralis priraum substantiae cellularis disperditione evanida, dein 

 sedimento cylindrum lignosum intus vacuum cumulorite substitula 

 et tune post ligni circumfusi abolitionem cylindrum plenum plus 

 minusve compressum fasciculorum meatuumque impressionibus 

 superficialiter notatum efformans." 



In cases where we cannot be certain as to the relation between 

 casts of the pith cavity and those of the cortical surface of a stem, 

 it will be convenient to make use of Saporta' s genus as a useful 

 designation to express the absence of sufficient data for any 

 more accurate identification. In some specimens we have the 

 clathrarian pith cast enclosed in a bucklandian cortex, but in 

 most cases the internal and external casts have been separated. 

 Although very probably, as Carruthers suggests, the detached 

 pith casts belong to more than one species of Bucklandia, yet 

 the very striking resemblance between those internal casts, which 

 are still surrounded by the cortical surface, and the isolated 

 specimens is sufficient reason for the inclusion of such forms 

 under the present genus. Hosius and von der Marck 2 have 

 described an Aptien fossil stem as Clathraria (?) galtiana, and 

 compare it with Clathraria Lyelli as figured by Schenk 3 ; it is, 

 however, probably not identical with the English type, and 

 should perhaps be referred to the genus Fittonia. 



8262. Figured by Stokes and Webb, Trans. Geol. Soc. [2] 

 vol. i. pi. xlv. fig. 1. Mantell, Illust. Geol. Sussex, pi. ii. fig. I. 4 

 Carruthers, Trans. Linn. Soc. vol. xxvi. pi. liv. fig. 3. 



From one end of the specimen the cast of the hollow pith 

 projects beyond the encasing wood and cortex; it shows the 



1 Loc. cit. p. 331. 



2 (A. 1), Palseontographica, vol. xxvi. pi. xlii. fig. 180. 



3 (A. 2), Palneontographica, vol. xix. pi. xxx. fig. 7. 



4 Mantell explains the repetition of Stokes and "Webb's plates in his "Illus- 

 trations of the Geology of Sussex " in a note on page 52 of that work. 



