586 ON TRIPLOSPORITE, 



veiy gradually tapering towards the top. As brought to 

 England it was not quite two inches in length ; but a 

 transverse slice, probably of no great thickness, had been 

 removed fi'ora it in Paris : the transverse diameter of the 

 lower slices somewhat exceeded the length of the specimen ; 

 470] its surface, which was evidently waterworn, is marked 

 with closely-approximated hexagonal arese, of which the four 

 lateral sides are nearly twice the length of the upper and 

 lower : these hexagons, which are the waterworn termina- 

 tions of the bractese of the Strobilus, becoming gradually 

 smaller and less distinct towards the top. 



A transverse section of the Strobilus exhibits a cen- 

 tral axis, from which radii directly proceed, constantly 

 thirteen in number, resembling, when perfect, the spokes of 

 a wheel, but several of them being always more or less 

 incomplete. These radii alternate with an equal number of 

 oblong bodies, also radiating, of a lighter colour, and which 

 are not directly connected with the axis : beyond these 

 twenty-six radiating bodies a double series of somewhat 

 rhomboidal areolae exist. These appearances not readily 

 indicating the actual structure in the transverse, are satis- 

 factorily explained by the vertical section. 



From the vertical section it appears that the Strobilus is 

 formed of a central axis of small diameter compared with 

 the parts proceeding from it, which consist, — 



1. Of bracteae densely approximated and much imbri- 

 cated ; the lower half of each of these stands at right 

 angles to the axis, while the imbricating portion, of about 

 equal length with the lower, and forming an obtuse angle 

 with it, is gradually thickened upw^ards : these form the 

 spokes and external rhomboidal arese of the transverse 

 section. 



2. Of an equal number of oblong bodies of a lighter 

 colour and more transparent, each of which is adnate and 

 connected by cellular tissue with the upper surface of the 

 supporting bractea. These bodies are sections of Sjoorangia 

 filled with innumerable microscopic spondes, originally con- 

 nected in threes (very rarely in fours), but ultimately sepa- 

 rating, as shown in Tab. 35 (XXIV), ?i^. G. 



