ON THE STRUCTURE AND AFFINITIES OF METACLEPSYDROPSIS DUPLEX. 165 
the specimens in one block. In the siliceous masses, on the other hand, there are 
singularly few genera, and at first sight this lends weight to the evidence of association. 
There was, however, another member of the Zygopterideze present—Stauropteris burnt- 
islandica, P. Bertrand,—and therefore the evidence of mere association must be dis- 
carded. The other genera present in the block were Botryopteris antiqua, Kidston ; 
Lepidophloios Scott, Gordon ; Lepidostrobus cylindricus, Gordon in MS. ; Lepido- 
carpon Wildianum, Scott; Bensonites fusiformis, R. Scott; and Stigmaria ficordes, 
Brongn. 
In the meantime Miss Benson, D.Sc., F.L.S., had discovered a similar stem, also 
associated with numerous petioles of Metaclepsydropsis duplex, in one of the calcareous 
blocks from Pettycur. In her subsequent investigation Miss Benson obtained “a 
considerable amount of the stem (22 inches) without securing any well-preserved 
nodes.” * A petiole-trace was closely associated with this stem towards one end, but, 
unfortunately, the stem emerged on the surface of the block just as the petiole-trace 
became fused with it. The specimen, which Miss Benson very kindly placed at my 
disposal and which is a co-type with my own specimens, illustrates clearly the great 
length of the internodes in this species, and proves the distance between two nodes, in 
some cases, to be at least 22 inches. 
Fragments of petioles of Metaclepsydropsis duplex were exceedingly numerous in 
the silicified blocks, but they were usually of no great length. Some were about 
8 inches long, but many did not exceed 3 inches, while others were under 1 inch in length. 
Most of these petioles were crushed, but often there were short lengths which showed 
no crushing. There were so many specimens that, by choosing the uncrushed portions 
only, a complete picture of the anatomy of the genus could be obtained. One remark- 
able feature about the specimens is that very few would be classed as normal petioles 
of M. duplex, and yet they would never be referred to any other genus, as will be 
seen later. 
By October 1910 sutficient positive evidence had been obtained to refer the stems 
found in the block to M. duplex. The more perfect specimens figured here were not 
discovered, however, until January 1911. Since then the early stages of petiolar 
development have been ascertained. The preparations examined number about 220. 
Most of these were prepared by myself, in order that nothing important might be 
lost during the process of preparation. As a rule the slides number 12 to 14 per 
inch of material, and they are generally in fairly long series. ‘The series showing the 
branching of the stem and the departure of the petiole-trace was obtained from a piece 
of stem 3 inches long. From this piece 39 sections (including two longitudinal sections 
each + inch long) were prepared; the sections were cut very close together, and run 
about 16 to the inch. 
Apart from the silicified specimens, I have made several series of sections from 
calcified examples as they happened to illustrate points not shown in the case of the 
* Letter, 17th May 1911. 
