330 NEW YORK STATE MUSEUM 



Formation of the leaf cushions in vertical rows. Traces of the 

 leaf cushions, in distant, irregular and generally oblique rows may 

 be seen down to within 5 cm of the basal periphery of the speci- 

 men. In passing upward they become more clearly defined, P, 

 plate 4, on narrow ridges which, higher still, plate 5, become more 

 prominent and more distinctly linear as well as more numerous. 

 Accompanying the rapid contraction of the bole in passing upward 

 the leaf cushion rows become more regular and closer, as is shown 

 in plate 5. The zone of plate 5, 25 to 50 cm above the base of the 

 trunk, is the region of most rapid increase in the number of the 

 cushion rows, as well as of rapid decrease in the diameter of the 

 trunk. The introduction of new rows of leaf cushions, i. e. of 

 new ribs, is distinctly shown at R on plate 6, in which we have 

 about 23 rows at the upper end within a longitudinal zone embrac- 

 ing but 10 rows at the lower border. At the level of the upper 

 border of the plate the impression shows 44 rows on one side of 

 the stem. It is difficult to ascertain exactly the number of rows 

 on the lower portion of the trunk ; but on the level of the middle of 

 plate 4, about 45 cm lower, there appear to be but 16 or 17 rows 

 on the impression. 



Region of sigillarioid leaf cushions. The upper part of the 

 area in plate 5, and the area situated about 5 cm higher, shown in 

 plate 6, exhibit the passage from the distant and irregular leaf 

 cushion row to the arrangement of the cushions in close, parallel, 

 vertical rows, each occupying the medial zone on the highly convex 

 surface of a longitudinal rib, an arrangement characteristic of the 

 ribbed Sigillariae. It 'may further be noted that in the upper part 

 of this plate the leaf cushions, S, occupying the greater portion of 

 the width of the rib, are, in the same row, separated by well defined, 

 narrow, transverse furrows which effect a partial segmentation of 

 the rib, while the ribs are separated by sharply defined, narrow, 

 angular furrows, thus presenting the characteristics of the favu- 

 larian section of the great Rhytidolepis group of the Carbonic 

 Sigillariae, with the exceptions of the differences in the leaf scar 

 itself, and the phyllotaxial angle. The similarity to the ribbed 

 Sigillariae is further seen in the parallel hypodermal strands, which 

 in the partially macerated portions of the cortex are seen to traverse 

 the slightly zigzag intercostal furrows, H, plate 6. 



From the level of the area shown in plate 6, the distinctly sigil- 

 larioid type of cortex with the leaf cushions on narrow longitudinal 

 ribs continues for some distance, while the ribs themselves become 



