STEUCTUEE OF LEPIDOSTEOBUS. 361 



I will now pass to the sections forming the principal subject matter of this communi- 

 cation, beginning with Lepidostrobus oldhamius as being the most completely known form. 



LEriDOSTROBUS OLDHAMITJS, Will. (a). 



This form is based^on four slides, three of which (C.N. 572, 1613, 1613 c^) are contained 

 in the Williamson Collection, and the fourth (S. 85) in that of Dr. Scott, F.R.S. The 

 sections are all isolated, i. e. there is no evidence as to whether they all belong to 

 different specimens or not. The longitudinal sections are only fragments, and include 

 neither the base nor apex of the cone, so that it is impossible to give any idea as to its 

 length, &c. The diameter of the transverse sections is between 2 and 3 centims. The 

 central axis of the cone has a diameter varying in the two transverse sections between 

 about 3*5 millims. (S. 85) and 4-0 millims. (C.N. 1613 d) ; that of the central vascular 

 cylinder being "7 millim. (S. 85) and '75 millim. (C.N. 1613 d) respectively. 



These slides are specially valuable for the perfect preservation of some of the axial 

 structures, the sporophylls and sporangia being only imperfectly shown : Wild's Cone, on 

 the contrary, exhibits well the structure of the appendages, and it is hoped that by a 

 combination of the two forms the structure of Lepidostrobus may be made out in a 

 fairly complete manner, although it must be admitted that there are still considerable 

 lacunae in our knowledge which can only be obliterated by the discovery of yet more 

 perfect remains. 



The general arrangement of parts is quite similar to that of L. oldhamius as described 

 by Williamson (the /3 form in the present paper), as will be seen by comparing his 

 figures before quoted with those in Plates XXXVI. and XXXVIL 



PI. XXXVI. fig. 1 is a partial transverse section of the cone, showing at m the pith-cavity 

 surrounded by the vascular cylinder x. The stele evidently contained a relatively large 

 medulla (larger than in the /3 form), although, unfortunately, in neither of the transverse 

 sections are any of the pith-cells preserved ; while the longitudinal section (C.N. 1613), 

 in which the anatomical structure is best seen, is not sufficiently radial to pass through 

 the medulla. 



Outside the wood is an empty space, i.s., from which the softer tissues (probably 

 phloem and pericycle) have perished. Leaf-trace bundles are seen passing through this 

 space. Beyond this, the usual three zones of the cortex can be recognized: i.e., the 

 inner cortex, with leaf-trace bundles passing through it; m.c, the middle cortical space, 

 with transverse sections of the leaf-traces l.t., each surrounded by a parenchymatous 

 sheath; and o.c, the outer cortex. Around the axis are shown sections of sporophylls 

 sph., and remains of sporangia with spores, sm. 



The Vascular Cylinder, ^c. — As in L. oldhamius (/3), the smaller xylem elements 

 constitute a peripheral zone with which the xylem of the leaf-traces is continuous. 

 Comparison of PI. XXXVI. fig. 2 with the similar section of L. oldhamius (/3) shown on 

 PL XXXVII. fig. 23 exhibits at once a difference in the number of the larger xylem 

 elements in the radial direction. In the former the average number of such elements is 

 but 2 or 3, sometimes reduced to 1 ; whereas in the latter they number 4-6. 



