shows an actual fossil natural size; (B) shows a few 
radiating lines of outer-wall-pore-casts seen from the inner 
surface x 10; this shows that the pores are much larger 
than those of H. tertius; those near the centres of radia- 
tion slope outwards and towards the centres, and some of 
them branch as they pass outwards; those in the middle 
(b) between two centres of radiation have two or more 
branches which diverge outwardly towards the centres of 
radiation; at (a) (a) are seen two connecting rods each 
surrounded by an incrustation of secondary silica; (C) 
shows a wax squeeze of the natural cast of the inner 
wall x 6; (D) a reconstructed transverse section x 6. 
CYATHOSPONGIA (Okulitch). 
? Order METACYATHINA (Bedford). 
۶ Family. 
New Genus Sigmocyathus. 
In 1910 T. Griffith Taylor described some fragments 
under the name of Coscinocyathus didymoteichus; no 
tabulae were visible in these fragments, so that the attri- 
bution to the genus Coscinocyathus was conjectural. We 
have found additional material which shows that the 
species attains a very large size, that no tabulae are 
present, and that it grows from a Metacyathus-like base. 
We propose to form a new genus Sigmocyathus for this 
fossil. Its family position, and whether it should be 
linked up with other genera, is left open for the moment; 
in our second memoir we described a form Sigmofungia 
flindersi, which we at first were inclined to place with the ` 
Metacyathina, but afterwards placed with the Spirocya- 
thina on account of the presence of synapticulae; 
Sigmocyathus has sigmoidally curved plates in both walls, 
and these plates are continuous, whereas Sigmofungia 
has sigmoid plates only in the inner wall, and these 
plates are not continuous, but isolated within the pores; 
continuous sigmoid plates are also found in Broncho- 
cyathus, a form described later in the present paper, 
which grows from a normal Archaeocyathus-like spitz, 
as well as in Vologdin's Siberian genus Cyclocyathus, and 
in Sigmocoscinus, which is described in the present paper. 
Among these several forms with sigmoid plates, con- 
vergent evolution, to which reference was made in our 
second paper, has apparently again to be considered. 
It therefore seems best to defer more precise placing of 
Sigmocyathus until a complete revision of the classifica- 
tion can be attempted. 
New Genus Sigmocyathus. 
May be defined as large turbinate cups with numerous 
straight septa, without synapticulae or tabulae, the inner 
wall. or both walls, possess continuous annular 
sigmoidally-curved plates; growth is from an irregular 
base of trabecular and vesicular tissue which fills the 
central cavity and obliterates the septa. The genotype 
is Sigmocyathus didymoteichus, the only species yet 
described. [ 
28 
Sigmocyathus didymoteichus=Coscinocyathus 
didymoteichus (Taylor). 
Drawings to supplement Taylor’s figures and descrip- 
tions are given in Plate XXII, Fig. 93, and Plate XXIII, 
Fig. 94. Fig. 94 (B) is a reconstruction of the complete 
fossil, natural size. Fig. 94 (A) shows an oblique 
longitudinal section of the Metacyathus-like base; the 
specimen from which this was drawn, the only base we 
have found, is almost entirely unsilicified, and is rather 
difficult to interpret in detail; the drawing is therefore 
diagrammatic. Fig. 93 (A) shows a transverse section 
of the normally septate upper part. Fig. 93 (B) a 
radial longitudinal section; the septal pores are oval or 
slit-like and are in about ten longitudinal rows, the 
central rows being straight up and down, whilst the 
inner rows slope upwards and inwards and the outer rows 
upwards and outwards; as these sloping rows die away 
on reaching the walls, fresh rows are interpolated in the 
more central regions to take their place. Fig. 93 (C) 
shows a surface view of the outer wall, and Fig. 93 (D) 
a view of the same wall from the septal side. Fig. 93 
(E) shows the inner wall, internal view. From these 
figures the nature of the sigmoid plates and their relation 
to the wall-pores can readily be seen. 
? Order SPIROCYATHINA (Bedford). 
? Family SPIROCYATHIDAE (Taylor). 
New Genus Beltanacyathus. 
Large conical cups with remote, coarse-pored septa; 
The outer wall an irregular fine mesh carried by an 
underlying coarser mesh; the inner wall composed of 
exceedingly large regularly arranged ‘canals leading 
upwards and inwards into the central cavity. Hori- 
zontal external flanges are not developed, but coarse 
vertical fluting may be present. Genotype, Beltanacyathus 
ionicus. 
New Species Beltanacyathus ionicus. 
This large and handsome form occurs in a small out- 
crop of poorly silicified material near the “Paint Mine,” 
Beltana, about a mile distant from the Ajax Mine. The 
cup attained a height of 15 cm. and a diameter of.7 cm., 
the intervallum coefficient being 25 mm.: 20 mm. Coarse 
vertical flutings are present externally. The septa are 
straight and remote, about 24 complete septa being 
present, but, between these, numerous incomplete septa 
extend inwards for various distances from the outer wall; 
every gradation is found between more or less complete 
septa and mere vertical ridges on the inner surface of 
the outer wall, these ridges being about 1 mm. apart 
and breaking up into an irregular network, over 3 mm. 
thick, pierced by pores about 2 to the mm. which slope 
upwards and outwards. The outer surface of this porous 
network gives off a multitude of minute branching 
papillae (see Fig. 96 (B), (C) ), which form a fine 
spongy external covering to the pores. The fragment 
shown in Fig 96 (A) appears to be from the top of a 
cup; it indicates a rapid expansion in size at the top; 
a part of the upper surface appears to be covered by a 
