3 X 4 
R. C. McLean. 
the interior, frequently containing dark material, while the central 
portion, which is sunk between the swelling lateral lobes, is badly 
preserved and full of dirt, so that its structure is difficult to make 
out. Nothing which might he considered an apical cell is to he 
seen, but the cells of the centre are all smaller than those of the 
lobes. 
The arched “ ventral ” surface, that turned towards the 
interior of the spore, does not seem, as preserved, to have been a 
surface during life, for its irregular nature suggests that the 
original surface has perished, and there are faint traces of tissue 
to be seen beneath it within the cavity of the spore, which 
increase this probability. 
Sunken in the tissue of the prothallus, are preserved the 
vesicles supposed to represent the archegonia. There are three 
which are more or less conspicuous, and two more doubtful 
examples, hidden in the dirt, which masks the central mass of 
tissue. 
The three with which we are concerned show nothing of a 
neck, they represent merely the egg-cavities. By means of experi¬ 
mentation on plasticine models, using the figures published by 
Gordon (see below) as a guide, it was possible to determine that 
the plane of the section lies at an angle of approximately 40% 
to the axes of the archegonia. Consequently nothing is seen of 
the necks, save some indication in the shape of the vesicles as to 
where they were attached. These vesicles are not surrounded by 
any special sheath, but are distinguished from the surrounding 
tissue only by their conspicuously larger size and thicker walls. 
They are so deeply sunken in the prothallus, and so remote from 
its surface, as represented in the plane of the section, that one is 
obliged to suppose their connection with the exterior world to 
have been in some other direction than in that plane. 
One of those in the central region shows what may have been 
the base of its neck, indistinctly visible. The vesicles vary in 
shape, the uppermost being somewhat longer than the others, but 
this may be due to variation in the direction along which the 
section cuts them, the latter being cut more longitudinally than the 
others. The walls of all are deeply stained. The way in which 
the lowermost is placed, with relation to the labia of the spore- 
coat, suggests that the whole prothallus has been pushed to some 
extent downwards into the spore-mouth during fossilization. 
