946 PROFESSOR W. U0. WILLIAMSON AND DR. D. H. SCOTT ON THE 
Sphenophyllum with the elaborate sporocarp of a Marsilia, which is obviously a 
highly specialized foliar structure, containing two series of sori, with numerous 
sporangia in each sorus. Whatever view be taken of the pedicel, we see no reason to 
doubt that the sporangium of Sphenophyllum is simply a single sporangium and 
nothing more. 
The comparison suggested with the Ophioglosseze is based partly on the ventral 
position of the pedicel, partly on the apparently eusporangiate character of the 
sporangium, which could scarcely have arisen from a single cell. In order to carry 
out the comparison we should have to imagine the fertile spike of an Ophioglossum 
bearing a single sporangium. Here again the resemblance seems to us too remote to 
be suggestive of affinity. 
We must be content for the present to leave this remarkable genus in its isolated 
position, in the hope that the extensive knowledge of its organization, which we now 
possess, may in the future afford an adequate basis for comparison, when additional 
forms of paleeozoic Cryptogams shall have been brought to light. 
In concluding this paper, we desire to acknowledge the essential help of those 
gentlemen who have contributed the illustrations. 
All the drawings reproduced in Plates 77 to 85 are the work of Mr. GkorGE BREBNER, 
formerly Marshall Scholar in Biology at the Royal College of Science, London. 
Of the micro-photographs, occupying Plates 72 to 76, the first two were taken by 
Professor J. B. Farmer, of the Royal College of Science, while all the rest, 24 in 
number, are the work of Mr. A. E. Turron, Demonstrator in Chemistry at the same 
College. 
The seven photographs in Plate 86, representing medullary casts of Calamites, 
were kindly taken for us by Mr. A. Gepp, of the British Museum, Natural History 
Department. For the loan of these specimens for photographic purposes, we have 
been indebted partly to Dr. Woopwarp and partly to Mr. CARRUTHERS, 
EXPLANATION OF PLATES 72-86. 
PLATES 72-76.—Photographs from the actual sections. Many of the photographs 
need to be examined with a lens. 
PLATE 72. 
Calamites. 
Photograph 1. Transverse section of a very young twig, corticated. Seven vascular 
bundles are shown, each with a large canal on its inner side. Primary 
structure still unchanged. C.N. 1020. x about 60. See also Plate 77, fig. 2. 
Photograph 2. Transverse section of a larger branch, with 19 vascular bundles ; 
