we propose the new generic name Rhizacyathus, with 
Rhizacyathus radix as genotype. The form may per- 
haps be regarded as one modified from Monocyathus. , 
Family Rhabdocyathidae, Vologdin. 
The family includes three genera of relatively simple 
construction, viz., Rhabdocyathus Toll, Rhabdocyathella 
Vologdin, and Yakovlevia Vologdin. We give in Plate 
XLII, Fig. 163, a rough sketch E Graz in trans- 
verse section, after one of Vologdin's. figures. 
Summary of Order MONOCYATHINA. 
Family Monocyathidae, Bedford. 
All the species known so far have been described by 
us from the Ajax Mine. They fall into three groups, 
but we await further knowledge before distinguishing 
them generically. i 
First group; tube at first continuous, later with scat- 
tered pores: Monocyathus irregularis. 
Second group; tube with regular pores in quincunx: 
M. porosus (the genotype), M. robustus, M. sparsipora. 
Third group; tube-wall reticular: M. spinosus, M. 
Mellifer (? 2nd or 3rd group). 
Of doubtful affinity: T'unkia incerta. 
Family Archaeophyllidae, Vologdin, Genera, Archaeo- 
phyllum and Butovia, Vologdin. 
Family Rhizacyathidae, Bedford. Genus Rhizacyathus, 
Bedford, 
‘Family Rhabdocyathidae, Vologdin. 
cyathus, Toll; | Rhabdocyathella 
Vologdin. 
Genera Rhabdo- 
and Yakovlevia, 
Order ACANTHINOCY ATHINA, Okulitch. 
The order was established by Okulitch, 1935, on the 
family Acanthinocyathidae, Bedford, 1934. 
The names Acanthocyathus, etc., first given were found 
to be preoccupied, and Acanthinocyathus, etc., were sub- 
stituted. 
The specimens agree with normal Archaeos in the 
possession of two walls; these are united by a very 
scanty framework of delicate radial rods. The inner 
wall is a very open simple polygonal net. The outer 
wall is built up, as it were, of a series of fused spicular 
elements enclosing large open spaces; spines or tubercles 
often project outwards beyond the general wall surface. 
The spitz, so far as known, has the same open net-like 
‚structure, 
Spitz of Acanthinocyathus. 
The smallest spitz found of this group is illustrated in 
Plate XLII, Fig. 166. It is a fragment 9 mm. long, 3 mm. 
"diameter at the upper and 1 mm. at the lower anl The 
- fragment is well preserved; it shows the outer wall as 
a loose open net along the whole length of the specimen; 
the characteristic inner wall is actually seen down to a 
point within about 3 mm. of the tip, trom which point | 
downwards the inner wall is shaved away in the speci- 
men, but, from the presence of radial rods, the existence 
of the inner wall to within a mm. or so of the tip can be 
inferred; the two walls are connected, as in the adult, 
by sparsely scattered delicate radial rods. i 
The simplicity of structure, open texture, and con- 
tinuity of character down nearly to the end of the spitz, 
together with the absence at all points of anything in 
the nature of a sheet-like structure perforated by pores, 
form a combination of qualities which separate this 
from all other groups of the Archaeos, and suggest a 
line of evolution from some such single-walled form as 
Monocyathus spinosus. : 
7 Acanthinocyathus transiens, sp. nov. 
In Plate XLII, Fig. 167, is illustrated a fragment from 
the Ajax Mine, which, whilst differing from previously - 
resemblance to 
described species, has 
Acanthinocyathus. 
points of 
It is too fragmentary for complete: 
description, but the outer wall is of an irregular net. ` 
work type, and delicate, more or less radial, sparsely 
distributed rods proceed inwards from the mesh. These 
rods, however, appear occasionally to anastomose, which 
is never the case in .ل‎ apertus. The specimen is too 
fragmentary to make it clear whether a defined inner : 
wall (as in Acanthinocyathus) is present. 
Summary of Order S R 
The species so far described are all from the Ajax 
Mine; they comprise: 
Acanthinocyathus apertus. 
? Acanthinocyathus transiens sp. nov. 
Pinacocyathus spicularis. 
New Order AJACICYATHINA. 
Examination of a number of spitzes of various species 
shows that members of that large group of Archaeos 
which includes not only the most regular and charac- ` 
teristic forms with porous outer and inner walls and 
straight porous plate-like septa, but also numerous 
forms with rod-like bars in the intervallum, originate in 
a spitz of a certain well-defined type, as described below. 
All the members of this group may be considered as: 
forming a natural order. 
The nomenclature of the group has come to present 
considerable difficulty. Taking first those typical | 
Archaeos with straight septa which are developed from . 
such a spitz, and finding, as we have done, that not all 
Archaeos with straight septa develop from such a spitz, 
what generic nama is to be applied to those typical ` 
Archaeos? 
In recent years most workers have drifted into thes 
