56 Dr. W. C. Williamson on 



W. " On some Anamolous Oolotic and Palaeozoic forms of vegeta- 



tion." Royal Institution of Great Britain, Weekly Evening 

 Meeting, Feb. 16, 1883. 



X. "On the relations of Calamites to Calamodendron," with 



description of an intermediate form. Memoirs of the 

 Manchester Literary and Philosophical Society, 3rd Series, 

 Vol. X., 1886-7. 



Y. A Monograph on ' ' the Morphology and Histology of Stigmaria 



ficoides." Palosontographical Society, Volume for 1886. 



Z. "On the Structure and Affinities of some Exogenous stems 



from the Coal measures." Monthly Microscopical Journal, 

 Aug. 1, 1869. 



A A. "On the Organisation of the Volkmannia (now Sphenophyllum 



Dawsoni). 



BB. XIX. Lepidodendron Harcourtii Brongniart, Halonia, Ulodendron, 

 Lepidophloios, Lepidostrobi, Lepidodendron Spenceri. 

 Phil. Trans., 1893. 



INTRODUCTION. 



The Carboniferous Plants that I propose to deal with in 

 Part III. of this Index are the Ferns. Seeing that fronds 

 of this group are so extremely abundant in most of the 

 shales and sandstones of the Coal measures, it might have 

 been expected that their stems, branches, and petioles would 

 be equally so in our calcareous nodules ; but, unfortunately, 

 this is not entirely the case ; yet they are not wholly 

 wanting, but such as we do obtain are usually fragments of 

 stems, petioles, and the secondary and ternary branches of 

 fronds. It is extremely rare to find any of these accom- 

 panied by their leaves or leaflets. Hence, it is often very 

 difficult to determine whether or not the objects we are 

 studying belong to the Filicine group. There are certain 

 well-known localities where fragments of stems are more 

 abundant than elsewhere, which stems unmistakeably belong 

 to the arborescent sections of the semi-tropical ferns. In 

 these examples their internal organisation is too character- 

 istic to leave much room for error respecting their primeval 

 affinities, but there are many forms which leave abundant 

 room for those differences of opinion respecting their true 

 relationship that are so common in the writings of even our 



