structures referred to as being a parasitic investment; 
and we propose the generic name Exocyathus for that 
type of investment which occurs in well preserved de- 
tail at the Ajax Mine, and also in other South Austra- 
lian localities. The genotype is Exocyathus australis. 
Various specimens are shown on Plates XXXIII to 
XXXV, Figs. 132-136. The tissue of Exocyathus consists 
in the main of a series of obliquely vertical lamellae, 
„which radiate from the Archaeo wall to which they are 
attached, and which, in a fully developed specimen, are 
arranged in a number of concentric zones. Under fav- 
orable conditions the tissue can be traced downwards 
into a small cylindrical body or bodies of very charac- 
teristic structure, shown in Fig. 132. These cylindrical 
bodies may be termed either “spitzes” or “roots” ac- 
cording as they are regarded as the first or the last 
stages in formation of the Exocyathus. If the struc- 
ture is regarded as “Exotheca,” and also if it is regarded 
as a parasite commencing as an outgrowth from the 
Archaeo, then these cylindrical bodies are distal “roots”; 
if, on the other hand, it is regarded as originating freely 
and becoming attached later as a parasite to the Archaeo, 
then the cylindrical bodies are proximal “spitzes.” It 
is impossible to be sure of this; a small specimen such 
as Fig. 132 A, B gives the impression of a spitz, but a 
spitz of very unusual kind, different from that of other 
groups of Archaeos; on the other hand Fig. 135 A and 
146 A, both of which show Exocyathus surrounding the 
bases of species of Archaeocyathus suggest that the 
cylindrical bodies are distal outgrowths from the zonza 
laminar masses. ; 
We make the provisional suggestion that the smali 
cylindrical form Fig. 132 A, B is the spitz of Exoc):uhus. 
that in course of growth the organism attaches itself 
parasitically to various species of Archavo, spreads in 
concentric zones Fig. 136 A and may give rise to more 
or less cylindrical outgrowths Fig. 135 A, 140 A. If 
this suggestion can be substantiated, it is clear thal the 
spitz is of a different construction from those found in 
other orders of Archaeos and may place Exocyathus in 
a separate ordere. - 
The question of the relationship of the various zoned 
and parasitic Archaeos is a very difficult one. Unless . 
structures are very definite, the correlation of silicified 
and unsilicified material is not easy. All one can say 
at present is that parasitism is suggested in the South 
Australian Exocyathus and that the form described by us 
in 1926 as Ajacia as a supposed Alga may be another 
parasitic Archaeo, Plate VII, Fig. 37; also in Vologdin’s 
Siberian genus. Labyrinthomorpha; also in the zoned 
outer tissue of the Canadian Archaeocyathus profun- 
dus. Zoned tissue is found in an irregular form in 
the South Australian Metacyathus taylori, and Metalde- 
tunorpha, and in more or less regular concentric zones 
in the South Australian Exocyathus and the outer tissue 
of the Canadian 4. profundus (see Bornemann’s photo- 
graph). As regards structural ‘indications of affinity 
Exocyathus, with its very distinctive “spitz,” appears 
quite different from Melaldetimorpha. which one is in- 
clined to relate to the Metacyathina: but the Paint Mine 
KI 
دن 
Metaldetimorpha is associated with zones having a re- 
semblance to Exocyathus (see Fig. 130 A, C, D, E. Bor- 
nemann's photograph of A. profundus has most resem- 
blance to the zoned tissue of the Paint Mine. Two 
questions which may be asked are: is the Paint Mine 
form a Metaldetimorpha or Metaldetimorpha plus Exo- 
cyathus? and: is Bornemann's photograph a Spirocya- 
thus plus Exocyathus or Spirocyathus plus Metaldeti- 
morpha? There is also another alternative, viz., that 
our Protopharetra furca Figs. 106 and 131, and the 4. 
profundus photographed by Bornemann are definite or- 
ganisms with a Protopharetra-like centre, surrounded by 
concentric zones of tissue; if this be so, they would 
appear to be related to Metacyathus taylori and Metal- 
detimorpha; but this does not seem to correlate them 
with the peculiar “spitz” structure of Exocyathus, and 
appears to hint at two distinct lines of development lead- 
ing to zoned structure in Archaeos; if P. furca is in- 
dividually one with its zoned surrounding tissue, then 
this tissue has a tendency to incorporate itself with or to 
parasitise other species Figs 106 A, 131 A, 
New Species Exocyathus australis. 
The Ajax variety of this species occurs as silicified 
cylindrical spitz-like fragments, Fig. 132, and as con- 
centric zones of laminar structure surrounding various 
species of Archaeos, Fig, 133, which often give off root- 
like bundles Fig. 146 A. The smallest specimens Fig. 
132 A, B consist outwardly of a close set series of ver- 
tical rods, spaced about five to two mm.; adjacent rods 
are connected by small and numerous cross-bars, thus 
constituting a kind of porous wall which differs markedly 
from that met with in any other group of Archaeos. 
Many of the rods are produced inwardly as lamellae 
which are elongated lengthways and which anastomose 
towards the centre to form long, irregular pipes. In 
somewhat larger specimens Fig. 132 C, the structure is 
more markedly lamellar and.less rod-like; and in still 
larger specimens the lamellae commence to have a zonal 
arrangement, Fig. 132 D. Fig. 133 A shows a trans- 
verse section of the lamellar structure, in two zones, 
attached to the outer wall of an Archaeocyathuss aequi- 
semis; the intimate relation of the structures, and the 
continuity of the wall pores of the Archaeo with the 
spaces of the Exocyathus are noticeable, Fig. 133 B 
shows a longitudinal view of the attachment in the same 
specimen. Fig. 133 C, from the same specimen, gives a 
longitudinal section of the. lamellar structure passing 
outward into a bundle similar to those shown in Fig. 
146 A, and Fig. 133 D shows a transverse section taken 
across A A in Fig. 133 C. In Fig. 134 A, B is seen 
a specimen of Metacoscinus reteseptatum. with a growth 
on the outer wall consisting of a kind of concentric 
"smear" of pellis-like tissue (a) within which are small 
Exocyathus-like lamellae (b). 
The variety of Exocyathus australis which occurs at 
Ardrossan has rather a finer texture, the laminae be- 
ing three or four to 1 mm. The material here is unsili- 
cified, but is excellently preserved. Fig. 135 A shows 
a transverse section of Exocyathus completely surround- 
