Mr. R. Kidston on Sphenopteris crassa. 119 



No pinnee are borne on the rachis below the bifurcation ; 

 but on the left-hand side of the left arm of the fork three 

 pinnas are given off (PL IV. fig. 1). On the right-hand side 

 of the same arm of the fork only one is produced ; but below 

 it we have two large cyclopteroid pinnules, which occupy an 

 analogous position on the stem to that of the pinnas. 



On either side of the axis, below the bifurcation, large cyclo- 

 pteroid pinnules are also situated, similar to those on the inner 

 side of the left and on the remaining fragment of the right- 

 hand arm of the bifurcation. 



On the highest pinna, the form of the pinnules changes 

 and assumes a rhomboidal outline, the margins being more 

 or less deeply cleft. 



The rachis shows little scars from which scales have pro- 

 bably fallen. 



On the specimen in the u Hugh-Miller Collection," one of 

 the pinna3 towards the lower part of the fossil shows the 

 cyclopteroid pinnules ; but on the greater portion of the speci- 

 men their form is rhomboidal (PL IV. fig. 2). 



The last-mentioned pinnules are composed of a number of 

 cuneate segments, united together in a fan-like manner, the 

 central one being the longest, on either side of which the 

 truncated apices of the segments give a dentate outline to the 

 pinnule, which is broadest near its centre. 



These must be regarded as the typical pinnules, the 



cy- 



clopteroid pinnules only occurring towards the base of the 

 frond. 



The difference between these two forms of pinnules is so 

 marked that, unless they had been observed on the same 

 frond, one would scarcely imagine that they belonged to the 

 same plant. 



In the figure of this species in the c Fossil Flora ' the dimor- 

 phic nature of the pinnules has not been brought out, though 

 on the specimen it is distinctly shown on the uppermost 

 pinna. 



The plant which Stur has described under the name of 

 Sphenopteris Kiowitzensis represents the middle part of a 



frond. 



His specimen likewise shows a dichotomy of the main axis, 

 as well as the dimorphic nature of the pinnules. 



In referring to the affinities of his specimens, Stur says : 

 11 Our plant shows almost as near a relationship with Spheno- 

 pteris crassa, L. & H., from the Carboniferous Limestone 

 of Burdiehouse. This has the rachis simple below, above 

 bifurcated, and bears pinnules, which likewise decrease from 

 above downwards (?). 



