related forms by the combination of a coarse intervallar 
structure with comparatively small inner wall pores. 
The wall is wavy in the lower part and passes into 
definite flanges in the upper part. The outer wali lias 
numerous small pores (Fig. 66C and Fig 67E), but, a* 
usual, these are often obscured. The principle of the 
construction of the intervallar tissue is shown schemati- 
cally in Fig 67, D, H, J; D being a radial longitudinal 
section; H an oblique transverse section in a plane 
parallel to e—g (Fig 67D); J an oblique transverse 
section in a plane parallel to Df (Fig. 67D). The 
structure may be visualised as a series of curved 
hexagonal-tubular lattices; these lattices are cut across 
in J, and are cut lengthwise in H; if the sections touch 
the rod-like elements of the lattice a radial ladder-like 
effect is given in H, or a hexagonal honeycomb in J; if 
the sections cut across the rods, a rectangular arrange- 
ment of dots is given in H, or a hexagonal arrangement 
in J. 
From this type of structure the various septal forms 
met with in the Spirocyathidae may be readily derived. 
Thickening of the two planes of mesh which approach 
the plane of the paper in Fig. 67D gives rise to wavy 
septa, and if the rods at right angles to the plane of the 
paper remain unmodified they appear as synaticulae; this 
condition is realised in Pycnoidocyathus synaticulosus. 
15 
Flattening of the septal waves and progressive disappear- : 
ance of the synapticulae results in Pycnoidocyathus 
sixplex and maximipora. A different modification, wita 
accentuation of the tubular character of the lattice, gives 
rise to Syringocnema. This type of structure explains 
the very misleading information given by a single chànce 
section of one of the Spirocyathidae; one and the same 
specimen, by a very small difference in orientation of 
the section, may appear to have definite radial structure 
or not; or it may show radial structure near the inner 
wall and Protopharetra-like structure near the outer wall, 
Or vice versa. 
Fig. 66 is from ane specimen; Fig. 67, A, E. F. from 
another; Fig 67K shows a longitudinal section of a spitz 
which is probably of this species. 
Fig. 68. 
The species was described by Taylor as Protopharetra 
rete. It is distinguished from similar species by the 
combination of a coarse intervallar mesh with a large- 
pored inner wall; the inner wall pores leading upwards 
and inwards into the central cavity. The upper part has 
marked flanges as in Pycnoidocyathus. The intervallar 
lissue is similar to that of S. ptychophragma. A shows 
an actual fossil, natural size; B a transverse; and C a 
radial longitudinal section. 
Spirocyathus rete. 
D, E are views of a spilz 
which is probably of this species, 
Genus PYCNOIDOCY ATHUS (Taylor). 
Taylor defines as “Cups in which the outer wall is 
thrown into deep horizontal bulges. Usually synapticu- 
late. Septa within the peripheral bulges highly 
irregular.” He places the genus in the family 
Archaeocyathidae. We have now given reasons for 
placing these forms in the  Spirocyathidae; P. 
ptychophragma has been referred by us to the genus 
Spirocyathus, and we confine the name Pycnoidocyathus 
to those forms which possess definite septa and show the 
deep bulges. 
Pycnoidocyathus synapticulosus (Taylor). Plate XV., 
Fig. 69. 
A shows a remarkably fine specimen, natural size; 
B shows the outer wall, C a transverse section, and E 
the inner wall of the same specimen. F shows the inner 
wall of an unusual variety in which the sloping plates 
leading upwards and inwards into the central cavity are 
replaced by simple bars. G is a transverse section of 
a variety in which the inner wall pores are considerably 
larger in proportion to the scale of niesh of the inter- 
vallar tissue. 
Pycnoidocyathus simplex (Taylor). Plate XV., Fig. 70. 
The figure shows a good specimen natural size. 
Pycnoidocyathus maximipora (Bedford). Plate XV., 
Fig. 71. 
The figure shows half of the type specimen, natural 
size. See also Part 1 page 3, and Plate II., Fig. 9. In 
this species the septa are almost completely flattened 
and the synapticulae have practically disappeared, but 
a little trabecular tissue still remains close to the outer 
wall, and the inner wall is markedly of the 
Spirocyathus-Pycnoidocyathus type. 
Pycnoidocyathus vicinisepta, N.Sp. Plate XVI., Fig. 72. 
The species has very clearly defined radial septa and 
synapticulae; the septa are much closer and the inner 
wall-pores smaller than in the previous species. A 
shows obverse and reverse views of the type specimen, 
natural size; B is a reconstruction from this specimen; 
C shows the inner wall, D a transverse section, and E a 
radial longitudinal section. F shows the outer wall, 
and G a radial longitudinal section near the base of 
another specimen. 
Pycnoidocyathus parvulus, N.Sp. Plate XVL, Fig. 73. 
This is a miniature edition of Pcynoidocyathus, 
being smaller in all respects than other species. 
A is a view of the type specimen, natural size. B shows 
a transverse section, C the inner wall pores and D a 
radial longitudinal section. 
