AND AFFINITIES OF STEPHANOSPERMUM. 363 
several grounds, whilst with the facts gained it may be possible to institute comparisons 
with other fossil seeds as well as with those of recent Gymnosperms. Taking first the 
general structure of S. akenioides, I shall proceed to a more detailed account of certain 
of its parts, and then, after describing the supposed new species, it will be possible to 
enter upon a more general discussion. 
STEPHANOSPERMUM AKENIOIDES, Brongn. 
General Structure. 
The seed is ellipsoidal in form, circular in transverse section, and, so far as could be 
ascertained, possesses perfect radial symmetry, saving only in respect of the archegonia, 
which appear to be developed in one plane only. The longitudinal section represented 
in Pl. 41. figs. LA and B is quite typical. The whole structure is limited externally by a 
hard testa (s£.), consisting largely of palisade-like stereides. This tegument, following the 
terminology of Brongniart, would be termed the endotesta, but, as there appears to be a 
layer internal to it, that term seems inappropriate. I shall speak of it as the sclerotesta, 
reserving the term endotesta for the more internally-placed soft layer. At the base of 
the seed the sclerotesta is relatively thick, and bears in median sections of good specimens 
a small papilla symmetrically placed upon its external surface (see Pl. 41. fig. 1 n, pa.). 
This is, no doubt, the point of attachment of the seed to the structure which bore it. At 
the papilla entered a delicate vascular bundle (v.5.) which, penetrating the testa, expands 
at the base of the nucellus into the basal tracheal plate (¢.d.). From the horizontal part 
of the testa springs the nucellus, which appears to stand freely within the integument. 
Above the insertion of the nucellus the sclerotesta thins out to its normal dimensions. 
At the apex of the seed it tapers to a long sharp beak, which is perforated by a canal, 
the micropyle (Pl. 41. fig. 14, m.). At the base of this beak the testa expands into a 
circular collar or crown with sharp edge directed forwards (c.). The top of the seed, 
between beak and crown, is occupied by a circular perimicropylar trough. 
Extreme length of seed from base to apex of beak 10 mm. Transverse diameter of 
seed at mid-height 4-4°5 mm. 
Within the testa we recognise the nucellus standing erect and apparently free within it. 
Towards the apex the nucellus tapers and seems to end in a beak or canal which engages 
with the micropyle. Between the nucellus and the testa a space is present, broadest 
around the upper fifth of the nucellus. The apex of the nucellus (the upper 4-1) is the 
pollen-chamber (p.c.). It is cut off by a conspicuous transverse membrane from its main 
body, which was almost entirely filled with a prothallium. The whole nucellus is limited 
externally by an epidermis usually characterised by the carbonised contents of its 
cells (ne.). Of the tissue composing the nucellus little remains in the prothallial region. 
The macrospore by its enlargement has invaded and compressed the nucellar wall to 
such an extent that with one exception little is recognisable beyond the epidermis and a 
few flattened layers. The exception, and it is a notable one, is the tracheal mantle. The 
delicate bundle which enters at the chalazal end of the seed (PI. 41. fig. 1 B, v.b.) expands 
into a wide tracheal plate, the margin of which is on every hand produced as a thin and 
2G2 
