70 GENERIC AND SPECIFIC CHARACTERS 



GENUS I. PEUCE. 



A medullary axis of ordinary size ; woody tissue consisting of elon- 

 gated cellules ; distinct concentric circles ; medullary rays ; bark. Stems 



roundish or compressed, tapering, branched. Pith of irregular polygonal 



cellules. Woody tissue in the transverse section presenting the appear- 

 ance of regular, parallel, radiating series of four-sided, subhexagonal cellules, 

 with interspersed narrow medullary rays. In the longitudinal sections, 

 the cellules are seen to be greatly elongated, with oblique dissepiments 

 placed at great distances. Two of the walls, those facing the medul- 

 lary rays, are marked with a single, sometimes a double series, of circular 

 areolae, more or less distant from each other. Those facing the pith and 

 the surface are continuous, and destitute of markings. The medullary rays, 

 in their transverse sections, usually present a single series of cellules. 



This genus is peculiar to the lias and oolite, at least no species have 

 been found in any anterior deposit. 



1 Pence Lindleiana. 



Areolae in one, sometimes in two, series ; medullary rays in their transverse 

 section of 1-8 cellules. 



Plate IX., lower half. Figs. 1, 2, 3, 4, 5. Probably also of Plate XIV. 



Figs. 1, 2, 3, 4, 5, 10, 12. Plate XV. Figs. 1, 2, 3. 

 From various parts of the Whitby Lias. 



2. Pence Huttoniana. 



Areolae in a single series ; medullary rays in their transverse section of 

 10-20 or more cellules. 



Plate XIV. Fig. 9. Plate XV. Figs. 4, 5. 

 Whitby Lias. 



