gastrula-like form, with two walls which are close 
together above, more widely separated below; عط‎ 
regarded Archaeocyathus and Spirocyathus as developed 
from this stage by widening of the intervallum and 
the appearance of septa. Neither in von Toll’s descrip- 
tion of Rhabdocyathus nor in his interpretation of it 
as an infolded gastrula is there any resemblance. what- 
ever to Monocyathus. Von Toll’s figures show two 
walls in the lower part, the outer wall being greatly 
thickened by concentric excrescences, and an intervallum 
, of considerable width between the walls, the intervallum 
. being traversed by little tubes. Double walls, inter- 
vallum and excrescences are all alike absent in 
Monocyathus. In an accompanying diagram the wall- 
pores are shown regularly arranged “in quadra"; this is 
quite different from the condition in Monocyathus, in^ 
which the wall-pores when regularly arranged 
invariably “in quincunx.” 
No doubt forms of Monocyathus have been or will be 
found in Siberia, but, if so, they cannot reasonably be 
referred to the quite different Rhabdocyathus as 
described by von Toll. 
are 
Spitzes of Monocyathus. 
Monocyathus. irregularis. One of the smallest 
Monocyathus spitzes seen diminishes, in a length of 7 
mm., from 14 mm. at the upper end to 4 mm. at the 
lower. It is figured in Plate XLII, Fig. 160. Though 
apparently broken at the lower end this is evidently very 
close to the extreme tip, and it indicates that the 
individual originates as a delicate irregular conical tube, 
probably closed at the tip as a little hemispherical cup 
of 4 mm. or less in diameter, for this seems to be the 
normal termination of the best preserved small Archaeo 
spitzes. Pores may be absent from the first 1 mm. or 
2 mm., and become scattered and fairly numerous as 
the distance from the tip increases. The pores in this 
species are in the main circular, irregular in size and 
distribution, and as a rule each pore occupies the summit 
of a little pimple or papilla. As will be seen later, 
such a simple conical tube, with or without pores at 
first, is the starting point in the growth of many, if 
not all, of the more highly organised regular Archaeos, 
in the ۰ young 'spitzes of which also the “papilliporous” 
condition i is often noticeable. 
Archaeo Spitzes in general. 
As regárds Archaeos in general we may say here that, 
though we have looked GOSE we have never yet 
seen in the Ajax Mine material any earlier larval stage 
than the single-walled conical tube; we have traced the 
best preserved: of many Archaeo spitzes down to hemi- 
spherical’ terminations of varying sizes, such as 4 and 
1/5 mm., and in one case 1/10 mm. 
IRE says (loc cit.) that a study .of Siberian 
material shows the Archaeo larvae to have been 
floating ts nearly ` skeleton- less organisms, 
and reached a size of 1/10 to 1/5 mm. 
1/100 mm. in diameter." These grew and "acquired a 
thin calcareous spheroidal hollow coating (the sphaerion 
stage) which is sometimes preserved in a fossi] state,” 
They became 
slightly elongated "gradually forming inside a second 
wall” (the dolium stage). With growth of. the 
"dolium" and increase in the weight of the skeleton, the 
organism settled to the bottom ond passed to the fixed 
life; growing upwards, the larva gradually developed 
into a conical calyx. “Stability oit the substratum was 
achieved by a subsequent growth of the base by means 
of additional skeletal elements or, in addition to this, 
by a filling of all the hollows of the lower part of the 
calyx with a calcareous skeletal mass.” 
1 
Our material has so far given no representation of a 
"sphaerion" stage, and, as regards a “dolium” stage, it 
shows on the contrary quite clearly that the inner Zoch 
actually arises within the developing conical single- 
walled ‘spitz at a time when the latter has attained a 
diameter usually of 3 to ł mm. — Okulitch (Trans. Roy. 
Soc. of Canada, 1935) figures serial transverse sections 
of small spitzes of regular Archaeos. He says “It is 
clear that the inner wall does not make its appearance |. 
simultaneously with the outer wall and the septa, but 
is a subsequent development." 
that Taylor's previously published sections (Memoirs of 
Roy. Soc. of S. Aus., 1910) are not typical, being made 
on material in which exothecal tissue and secondary 
silicification obscured the position. We 
nearly all points with Okulitch.: 
As regards the basal fixation referred to by Vologdin, 
the great majority of specimens from the Ajax Mine 
have no such indication, the spitzes being quite naked 
without structural means of attachment. There appears 
to be diversity in this respect in different Archaeo 
localities, and where, as in some localities, exothecal or, 
we have a suspicion . 
“root” structures are prevalent, 
that these are parasitic or encrusting organisms speci- 
fically distinct from the enclosed Archaeo. Considerable 
reference to this matter was made in our fourth memoir 
and we shall come to it again later. 
Several groups of Archaeos may well have evolved 
from an ancestral type corresponding to Monocyathus 
irregularis. A regularisation of the pores would give 
rise to Monocyathus porosus, and this, combined with the 
appearance of an inner wall and connecting rods would. 
lead first to Dictyocyathus-like forms and next, by con- 
centration of the rods in longitudinal rows, 
regular Archaeos. and further, 
to the 
by concentration both 
longitudinally and transversely, to Coscinocyathus and its 
relatives. Another line of evolution from the 
"Monocyathus irregularis: type, commencing with the 
appearance of imperforate transverse partitions in the 
tube and continuing with growth of trabeculae from. 
these partitions and from the wall would lead to the 
various forms of the Order Metacyathina. 
He also points out. 
agree in 
کا ا 
