verse section an appearance may be given like that of 
the inner wall of Coscinocyathus papillipora (Plate III, 
Fig. 19a) which we now place in the same genus Sigmo- 
coscinus. The mode of development of this type of 
inner wall is shown in the spitz now to be described, 
which is certainly of this genus and probably of the 
species papillipora. 
This spitz, illustrated in Plate XLVIII, Fig. 1997, has 
some remarkable features. When first exposqd the 
drawing Å was made of the surface, and also a trans- 
verse section B as seen on the edge of the stone, 
the total diameter being 33 mm. at the top of the spitz. 
Successive longitudinal grindings were then made, and 
the re-etched surfaces drawn at C, D, E, ‘more 
in width and more in length towards the spitz being 
‚exposed each time. The tangential section, C, through 
the intervallum of the upper part shows septa and 
'tabulae and the papilliporous outer wall pores. The 
tangential section, D, grazes the inner wall of the upper 
part of the spitz. The angle of grinding was then 
slightly changed in E, showing, at the top of the draw- 
ing, a nearly radial longitudinal section of the inner 
— wall about the middle of the spitz, and bringing out 
the sigmoid inner wall structure; the lower part of the 
drawing shows a longitudinal section grazing the lower 
‚part of the inner wall, this section extending to the 
hemispherical termination of the spitz, which is here 
. 14 mm. diameter; in this section transition is seen from 
"simple normal pores of the inner wall below to sig- 
- moidal pore-plates above. Septa do not appear to ex- 
tend to the lowest 3 mm. of the spitz, but two trans- 
verse structures, which, though apparently without pores 
in the intervallum, seem to represent tabulae, are present 
near the tip. Finally the tip of the spitz was ground 
away transversely to show three successive transverse 
sections, F, G, H, of the lowest part; F (at level F 
in E) shows the bottom of the tsner wall, seen from 
below, which is apparently closed, porous and tuber- 
culated; G (at level G in E) shows from below the 
. lowest "tabula," which appears to cross through the 
central cavity and to be without pores except for three 
within the central cavity; H (at level H of E) shows 
the porous inner wall; in none of these three sections 
have septa yet put in an appearance, and in all of them 
outer wall pores, if originally present, are obscured by 
_ siliceous thickening. 
Sigmocoscinus specimens are extremely rare, so that 
we were fortunate to find a spitz in such good condi- . 
. tion, and to be able to make out considerable detail; 
` at the same time, it is realised that, before building too 
` much on the information it gives, comparison with 
further specimens is much to be desired. Present infor- 
mation indicates, for this genus, a spitz which differs 
considerably from the Alphacyathus type, whilst differ- 
ing still more strongly from the Archaeopharetra spitz . 
of Metacyathina, 
"m 
3 
Order METACYATHINA, Bedford. 
This ordinal name was used in our second memoir 
(1936), but considerable additional intormation is now 
available. The spitz of Archaeopharetra type is now 
found to be the distinctive feature of the order. This 
spitz commences as a small conical tube with trans- 
verse partitions; as the tube enlarges rod-like processes 
grow from the partitions, and, later, the partitions 
appear to give rise to “dissepiments” and the rods to 
trabecular tissue, In some of the most characteristic 
members of the order, whilst the basal portions have 
the abovementioned trabecular and dissepimental struc- 
ture, without inner wall or central cavity, the upper 
portions develop inner wall and central cavity and the 
irregular trabecular tissue gives rise to clearly-defined 
radial septa. It now appears certain that regular sep- 
tate archaeos arise from spitzes of two distinct types, 
the Alphacyathus and Archaeopharetra types respec- 
tively, and that' knowledge of the embryology is essen- 
tial to a natural classification, The archaeos present 
some remarkable examples of convergence.. A com- 
plete system of classification is not yet attainable,. but, 
among forms of which only fragments of the adult form 
are known so far, it may be said that the following 
features suggest relationship to Metacyathina, viz.: 
synapticulae, dissepiments, compound-reticular and 
irregular walls “wire-netting” and coarse-pored septa; 
some of these features, however, are absent in upper 
parts of some species actually traced to Metacyathus- 
like bases. 
Family | Metacyathidae.- Bedford. 
Genus Archaeopharetra, Bedford. 
Some of the specimens described under this head 
are no doubt spitzes of other genera of Metacyathina, 
but the following new species Archaeopharetra 
vologdini has been traced from an Archaeopharetra 
spitz to a quite distinctive upper part. 
Archaeopharetra vologdini sp. nov. 
A spitz of this species is shown in Plate XLVIII, Fig. 
200. At A is exposed the lower part of the spitz in 
longitudinal section, most being just below the outer 
wall. This part contains about eight transverse parti- 
tions, with a few irregular protuberances and ranges 
from 2 mm. diameter above to 1 mm. below, Trans- 
verse sections of this part at levels B to G are shown 
in B to G. The spitz was then ground away further in 
the stone, giving sections I, J, and K. By the time the 
topmost section was reached, at 3 mm. diameter, a 
symmetrical structure had developed. The exterior has 
a fluted surface, resembling (? Archaeocyathellus) 
floreus, but the internal structure is far more open 
than that of Archaeocyathellus; the inner wall is a very 
open structure and. inner and outer walls are still con- 
nected by widely spaced rods rather than by septa. 
