plants from the Devonian rocks OF. 
The Thece. The thece occur in several different states of 
preservation. One of the best of these is seen on fig. 11, natural 
size, and enlarged on fig. 7 of Plate IV. It is attached to a long 
stalk or axis. The theca is cup-shaped, rather short and com- 
paratively broad. It measures about 8 mm. in length, and 1 cm. 
across at its widest part. Distally it is divided into at least eight 
lanceolate teeth, which are rather blunt. The teeth are about 
15 mm. long, Another specimen (fig. 6 of the same plate) 
also attached to a stalk 1-4 cm. in length, and showing some 
indications of a dichotomy below, is somewhat similar but broader. 
It exceeds 1 em. in length, and 11 mm. in breadth. The number 
of teeth is here uncertain, but they were at least eight, the points 
of which are broken off in nearly all cases. 
A curious specimen, of which we have more than one example, 
is seen, natural size, on fig. 2 and three times enlarged on fig. 1 of 
Plate IV. It shows the ultimate dichotomy of an axis, each branch 
(7—8 mm. long) ending in a theca, the form of which is obscure. 
The number of teeth is also uncertain. They were at least four 
in each case, probably more. The thecz, as well as the axis, are 
covered with a large number of minute oval or circular scars or 
prints. These consist of a small central elevation, then a broad 
circular depression, and finally an outer raised rim. A micro- 
scopic examination of these scars (two of which are shown 8 times 
enlarged on fig. 4) does not throw any more light on their origin 
and nature than can be ascertained by means of a hand-lens, and 
we are quite unable to explain them. 
The theca shown on fig. 5 of the same plate is of a somewhat 
different type. Only a small part of the axis is seen, and the 
theca is more sac-like in form and the teeth are longer. The 
entire theca is 11 cm. long, and 5°5 mm. across at its broadest 
part.. The teeth appear to be at least 5 mm. in length, and were 
probably more than six in number. This form is much narrower 
than in the case of those described above. It may be a distinct 
species, but on the whole we are inclined to include it, at least 
provisionally, under X. devonica. 
Finally we have some examples of apparently lobed thecz 
such as that seen on fig. 3 of Plate IV, where the divisions between 
the teeth extend nearly to the base in some cases, and only about 
half-way in others. How far this is to be regarded as a natural 
feature it is difficult to guess. On the whole we should be inclined 
to view such variations as at least partly due to accidents of pre- 
servation. It is conceivable of course that, when mature, the 
thecze might split open along more than one line, but the present 
material does not allow us to form any opinion as to whether this 
actually did or did not happen naturally. 
As to the real morphology of Xenotheca there is little or no 
