464 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
sizes, many of which are filled with black carbonaceous matter, c. I can detect no 
vessels in the section. The division of the central portion into four lacunar cavities 
reminds us of the similar divisions in the leaves of Isoetes. 
Psaronius Renaultii. 
In my memoir, Part YII., pp. 10-13, I described, under the above name, some 
sections which I believed to belong to an arborescent fern, and in fig. 22*'*, d, I 
represented the only trace of a vascular bundle hitherto met with belonging to this 
plant. Mr. George Wild, of the Bardsley Collieries, Ashton-under-Lyne, has since 
furnished me with a much finer specimen, a section of which is represented in fig. 16. 
The vascular bundle, a, is quite perfect, and corresponds both in shape and size with 
several of those represented by Corda, whilst the fragments of a second similar 
bundle at a' show that the section is but a portion of a large stem in which there 
has been at least one circle of similar bundles. Each of these vascular zones is 
enclosed within a thin phloem sheath, b, whilst the fundamental tissue exhibits the 
small gTim-canals, c, already described; some of these, c', are filled with carbonaceous 
matter. The size of the bundle at its greatest diameter is IT, the figure being 
enlarged about 2-| times. 
Zygosporites. 
In my memoir, Parts IX. and X., I described some minute objects under the above 
name, and whilst recognising their striking resemblance to the zygospores of several 
Desmideae, I declined to follow some of my French friends who regarded them as 
being true Desmids. A discovery by Mr. Spencer in the Halifax beds has justified 
my doing so. 
Fig. 17 represents an oblong sporangium containing several of these Zygosporites 
under conditions which leave no room for doubt that they are true spores. The 
sporangium is about '042 in length; fig. 17 being enlarged about 110 diameters. 
Fig. 18 represents the portion containing the zygospores, enlarged about 290 dia¬ 
meters. The spore, fig. 18, a, is obviously identical with the form which I designated 
Z. brevipes; but the peripheral radii in fig. 18, b, are longer than in my fig. 51 
(Memoir, Part X., Plate 19), and approach, in that respect, fig. 54 of the same plate, 
to which latter form I gave the name of Z. longipes, indicating that these are but 
extreme forms of one species. Other fragments now in my cabinet leave little, if any, 
doubt in my mind that these spores are identical with those of the fruit figured in my 
memoir, Part V., Plate 5, figs. 28, 29, and 30, under the name of Volhnannia Daw- 
sonir Under these circumstances the provisional name of Zygosporites may be can- 
* This fruit was assigned to the genus Volhmannia at a time when that genus was much clearly less 
defined than it now is. Brongniart, going further even than had previously been done by Unger, 
