32 



Prof. W. C. Williamson. 



[May 11, 



sonis. It was characterised by having a large cellular medulla, 

 surrounded by a thin vascular zone composed of short radiating 

 lamellae. This, in turn, was invested by a cylinder of cortical paren- 

 chyma from which radiated a number of thin cellular laminae, like 

 the spokes of a wheel, separating large lacunae. Each lamina 

 generally consisted of a single series of cells. At their peripheral 

 end, these laminae merged in a thick, large-celled, cortical parenchyma. 

 The generic name, Myriophylloides, was given to the plant because of 

 the resemblance between sections of its cortical tissues and those of 

 the recent Myriophyllum. Two reasons induced the author to object 

 to this name (" Nature," December 8, 1881 r p. 124), and to propose 

 the substitution of that of Helophyton. Such substitution, however, 

 was rendered unnecessary by the discovery, by Mr. Spencer, of Halifax, 

 of some additional specimens which indicate that the supposed new 

 plant was merely the corticated state of the Astromyelon, described 

 by the author in his Memoir, Part IX.* These specimens showed 

 that the plant was more complex than had been supposed, different 

 ramifications of it having individual peculiarities. 



In some of the new specimens the vasculo-medullary axes present 

 no differences from those of the Astromyelon already described. The 

 radiating lines of cells separating the lacunae prove to be transverse 

 sections of elongated vertical laminae composed of cells with a mural 

 arrangement, and which separate large vertical lacunae of varying 

 lengths ; a type of cortical tissue clearly indicating a plant of aquatic 

 habits. So far as this bark is concerned, all the ramifications of the plant 

 display similar features, but several of the specimens exhibit important 

 variations in the structure of the vasculo-medullary axis. In them 

 the central cellular medulla is replaced by an axial vascular bundle, 

 which has little, or in some examples apparently no, cellular element 

 intermingled with the vascular portions. In some examples this axial 

 bundle is invested by the thick exogenous zone seen in Astromyelon. 

 In others that zone is wholly wanting. Yet there appears to be no 

 reason for doubting that these are but varied states of the same 

 plant which branched freely, the differentiated branches having, doubt- 

 less, some morphological significances, as yet incapable of being 

 explained. That the plant was a Phanerogam allied to Myriophyllum 

 is most improbable. It has several features of resemblance to the 

 Cryptogamic Marsileae, from which it does not differ more widely 

 than the fossil Lepidodendra do from the living Lycopodiaceae. 



The author describes a new specimen of Psaronius Renaultii, found 

 by *Mr. Wild, of Ashton-under-Lyne. Those previously described 

 consisted almost entirely of fragments of the bark and its serial rootlets. 

 The present specimen contains a perfect C-shaped fibro-vascular 

 bundle and a portion of a second one, resembling some of those 

 * " Phil. Trans.," 1878. 



