166 W. T. GORDON 
siliceous petrifactions. For the sake of completeness, also, it is proposed to redescribe 
the species, particularly as previous accounts have been based on a few isolated sections 
from several distinct individual specimens, and thus several points have not been 
recorded. All previous work on this genus has been based on petioles whose xylem 
strand had an hour-glass shape, but I hope to show that this trace has been developed 
from a simpler type. : 
Metaclepsydropsis duplea was first recorded by WitiiaMson in 1874 under the 
name Kachiopteris duplex.* His specimens had the hourglass-shaped xylem strand so 
characteristic of the mature petiole. From 1874 until P. Berrranp’s description in 
1909 no further work was done on this genus, although it was constantly referred to. 
Kipston and Gwynne-VaucHaNn, in Part IV. of their memoir on the fossil Osmun- 
dacez,{ refer to Metaclepsydropsis, but have discussed its affinities rather than its 
anatomy. Apart from Kinston, no observer seems to have had more than a few isolated 
sections to deal with. Some years ago, however, Dr Kipsron had a particularly fine series 
prepared, and these he has kindly placed at my disposal. In addition to showing the 
anatomy so far as it is known, they exhibit the remains of aphlebie and the passage 
of the aphlebia-traces out to these organs (text-fig. 2). The unique opportunity I 
have had of studying numerous petioles of all sizes has resulted in the elucidation of 
the petiolar development. The material on which I have been working is practically 
a felted mass of petrified stems, roots, petioles, pinne, and pinnules of the species. All 
of them are fragmentary, but, by cutting series of sections from various individuals, 
a more or less continuous chain of development has been established. The extent of 
the overlapping in these series is shown in the following table :— 
Stage of Stage of Stage of Stage of Stage of Staye of 
MI Sig 6.\ Pill fig 33\ Pell fig32\ MM fig29 | Pell fig2/\ Pill fig 2s. 
MAT MhBe 
ZO} -IZ276 
Text-Fic, 1.—Diagram illustrating the extent to which the various series of sections overlap. These series consist 
of sections which only show early stages of the petiole-trace. 
* Phil. Trans, Roy. Soc., vol, elxiv., 1874. 
t Trans. Roy. Soc. Edin., vol. xlvii., 1910. 
