ef 
Gu 
vU 
openly reticular. 
Spitz of Monocyathus porosus, Bedford. 
The smallest spitz of Monocyathus porosus so far 
found is shown on Plate XLII, Fig. 161. Unfortunately 
this is still 2 mm. diameter at the smaller end, so that 
we are unable yet to say whether the regular arrange- 
ment of numerous pores in quincunx continues to the 
extreme tip. The absence of smaller spitzes of this 
form suggests a possibility that some of the specimens 
attributed to M. irregularis may be spitzes of M. porosus. 
but of course, until a specimen of M. porosus is found 
complete in its lower part, we have no direct evidence 
on this point. The most interesting feature of 
Monocyathus porosus (see our earlier figures, particu- 
larly Plate X, Fig. 46) is its strong resemblance to the 
outer wall of several of the regular Archaeos. 
Spitz of Monocyathus spinosus, Bedford. 
The spitz previously figured in Plate X, Fig. 50, was 
the first fragment found of this very scarce species; we 
have since found another fragment (Plate XLII, Fig. 
162) which well shows the very regular structure of the 
upper part. The construction is quite different from 
that of M. irregularis, for it consists of a regular trabe- 
‘cular mesh which encloses relatively large polygonal 
pores and has spines or tubercles projecting outwards. 
Whereas M. irregularis is at first essentially a continuous 
tube, M. spinosus has from the first a wall which is 
In this respect it may be perhaps 
regarded as the single walled ` prototype of the 
ı Acanthinocyathina. Monocyathus mellifer is a scarce 
' but well defined species; the wall is beautifully regular, 
the pores forming a honeycomb pattern; its structure is 
thus intermediate between that of M. porosus and M. 
spinosus. 
Note on the Order Monocyathina. 
Taylor, in his 1910 memoir, noticed fragments of these, 
saying “the shape reminds one of the primitive Olynthus 
of the sponges” and “‘it is possible that these organisms 
are mature sponges whose development has not proceeded 
further than the Olynthus stage.” Taylor does not relate 
sponges, whilst he is inclined to regard the Archaeos 
às primitive “Cambrian Metazoa" intermediate between 
sponges and corals; he says “it is suggested that . . . 
in the Archaeocyathinae we have evidence of the modifi- 
cations of the generalised type which gave rise to the 
'Calearea and Anthozoa." | 
. In 1934. we described two species Monocyathus porosus 
and M. irregularis, and related them to. the Archaeos as 
members of a new family Monocyathidae. — Okulitch in 
. 1935 gave this family ordinal rank as Monocyathina. He 
. placed the whole of the Archaeos in an independent class 
of the Porifera, and at first called this class Cyatho- 
spongia, but, finding the name preoccupied, changed it 
later to Pleospongia; Monocyathina ¿being the most 
- primitive order of the class and being regarded as 
69 
these forms to the Archaeos; he speaks of them as. 
l 
. wall being up to 12 mm. thick. 
2 species) and Butovia. 
representing the ancestral type of the more complex 
forms.  Ukulitch’s view of the general position of the 
Archaeos appears to be gaining more acceptance than 
any previously put forward. 1 
Tunkia incerta, Bedford. 
This very small organism is described in our third 
memoir (Sept. 1936). Although there is considerable 
resemblance to Monocyathus, we hesitate to class it with 
that group on account of the different state of preserva- 
tion. A photograph of this organism appears in a 
paper of March, 1937 (Neuen Jahrb. fur Mineralogie) 
by T. H. Ting, who worked on material from the Ajax 
Mine sent by us in exchange to Dr. Krantz, of Bonn. 
Ting refers the specimen, as Calathium sp, to the genus 
described by Billings in 1865. Billings considered his 
Calathium as related to Archaeocyathus and was 
inclined at first to regard both as protozoa and later 
(Pal. fossils I. p. 357) as sponges. The identity of 
Tunkia with Calathium is extremely improbable; 2 mm. 
is large for the diameter of Tunkia and 4 mm. for the 
pores, the wall being 1/5 mm. thick; whereas the 
Calathium specimens Ting refers to are from 20 mm. to 
60 mm. diameter and the pores 2 mm. diameter, the 
The extreme difference 
between the two genera may be at once realised by 
inspecting Billing’s figure of another species, Calathium 
anstedi (or crassum) (1 c. p. 337); we shall have 
occasion to refer to this figure later. 
_ Family Archaeophyllidae, Vologdin. 
Vologdin in 1931 described some conical or cornute 
cups, up to about 10 mm. diameter, characterised by a 
single wall with external as well as internal vertical 
ribs. He spoke of the wall as non-porous, but 
qualified this in 1937 by saying “one sometimes shows a 
porous structure." The cavity is traversed by numerous 
horizontal plates, slightly concave upwards; he spoke 
of these as tabulae and as continuous and thin near the 
wall, and passing in places into a sort of vesicular ` 
tissue. He described two genera, Archaeophyllum (with 
| We give.in Fig. 164 trans. 
and long. sections of Archaeophyllum sketched roughly 
from Vologdin’s figures. 1 
It may be of interest. to compare this single walled, 
non-porous type, having transverse partitions, with the 
“Archaeopharetra” spitz of Metacyathina. 
New Family Rhizacyathidae and genus Rhizacyathus. 
In our last memoir we described a little cylindrical 
form, Protopharetra radix; this has outer wall, but no 
inner wall or central cavity, the interior being occupied 
by anastomosing bars which have in the main a sloping 
longitudinal orientation. Transverse sections of a spitz 
of similar character are shown in Plate XLII, Fig. 165. 
This has the structure neither of a regular Archaeo spitz 
nor of a transversely partitioned Metacythine spitz, and 
