444 'Rev. S.VLa.VLghtou onCyciostigmn, aneiuGenusof FossilPlants. 



existed on the globe. Probably closely allied to the orders de- 

 scribed as Knorria, Lepidudendron, and Sigillaria. Known only 

 by their leaf-scars and leaves, which were arranged in alternate 

 whorls ; plants not jointed at the whorls ; the leaf-scars per- 

 fectly circular, showing in many cases a minute and well-marked 

 dot in the centre, probably coinciding with a central bundle of 

 woody tissue ; many of the larger plants show traces of a thick 

 central woody axis, like that found in Stifjmaria ; stems much 

 crushed and flattened, as if they were not woody through- 

 out. 



They approach nearest to Stigmariacea , from which they differ 

 in the leaf-whorls being further apart and more distinct. 



There are many varieties of this remarkable fossil, showing 

 the alternate whorled arrangement of leaf-scars. None of them 

 are perfect stems, but appear to be torn portions of the rind of 

 large plants which have been macerated by floating for a long 

 time in water. In the quarry at Kiltorcan the Cydostigma is 

 found in layers different from those in which the Cyclopteris 

 Hibernica occurs. 



In some specimens of Cydostigma the leaf-scars are closer 

 together than in the last, and are somewhat oblique to the 

 transverse line of the stem, — this obliquity being due to distor- 

 tion caused by lateral pressure of the mudstone in which the 

 fossils occur. The whorled arrangement of the leaves, each 

 whorl being alternate to that above and below it, is frequently 

 well shown. 



Cydostigma Kiltorkense. 



Stem (flattened) 3^ inches in diameter. Leaves in alternate 

 whorls, 25 in each whorl; whorls 1 inch apart. Divergence 



1 



•50- 



Central woody axis ^, inch in diameter (flattened), 

 shown by the strongly marked band in the centre of the stem. 

 This is the largest of the species of Cydostigma found at 

 Kiltorcan, and I have given its specific name from the locality. 



Cydostigma minutum. 



Leaves in alternate whorls, the whorls being somewhat more 

 distant from each other than the leaves; the centre of each leaf- 

 scar marked by a well-defined minute dot. Branches of stem 

 dichotomous. 



This is the species figured in Sir Charles Lyell's ' Manual,' 

 5th edition, p. 418. It is a well-marked and easily-recognized 

 fossil. It is also the same as the fossil figured by me in the 

 Journal of (ieol. Soc. Dubhn, vol. vi. p. 235, and named Lepi- 

 dodendron mimtlum. The latter was ibund at Tallow Bridge, 

 CO. Waterford. 



