at very remote intervals. Three specimens have been 
found, all with similar features. The species differs from 
D. simplicissimus in the outer wall being thicker than the 
inner, in the smaller and more uniform size of outer and 
inner wall-pores and the absence of connecting bars. 
New Order SPIROCY ۰ 
This Order represents a line of evolution distinct 
from the Archaeocyathina. Whereas the latter originate 
from a Monocyathus-like spitz with markedly perforate 
(outer) wall to which definite septa and perforate inner 
wall are quickly added, the simplest forms of the 
Spirocyathina, e.g., Dictyocyathus, possess an outer wall 
in which pores are usually masked by secondary 
silicification, a regularly perforate inner wall, and, 
connecting the two walls, at first radial rods and then a 
delicate network of anastomosing rods. From spitzes 
of this type we find developed in the family Spirocyathi- 
dae an intervallum system of hexagonal hollow lattices 
which, leaving the outer wall nearly horizontally curve 
: downwards as they proceed inwards towards the inner 
wall; concurrently with this development the inner wall 
pores are frequently converted into large channels 
leading upwards and inwards into the central cavity. 
From this condition two lines of evolution are fol- 
lowed. In one the side members of the hexagonal lattice 
become flattened and plate-like, to form septa, the top 
and bottom members of the lattice remaining as 
synapticulae, a condition seen in Pycnoidocyathus 
synapticulosus (Taylor), which we therefore remove 
from the Archaeocyathina and include in the present 
order; loss of the synapticulae results in Pycnoidocyathus 
maximipora (Bedford). In the other line of evolution 
the curved hexagonal lattice becomes defined as a curved 
hexagonal tube, as in Syringocnema favus (Taylor). 
The order presents a very clear case of convergent 
evolution, the septa of Pycnoidocyathus having a close 
resemblance to those of Archaeocyathus, but having a 
totally different mode of origin. There is good reason 
to believe that several other examples of convergent 
evolution occur within the class. ` Tabulae or tabula- 
like structures appear to have arisen several times quite 
independent of the Cosinocyathidae. Further research 
will be needed to define many points, but it is already 
clear that convergent evolution must be taken into 
account in classifying the Archaeos. 
We divide the Spirocyathina into five families, 
Dictyocyathidae, "` Dictyocoscinidae, ^ Spirocyathidae, 
Syringocnemidae. and Sigmofungidae. 
Family DICTYOCYATHIDAE (Taylor). 
After removing the genus Dokidocyathus from this 
family, there remains only the genus Dictyocyathus 
(Bornemann). Taylor defines the genus “Intervallum 
without continuous septa, and only united by numerous 
18 
rounded rod-like rafters." In the spitzes and the simpler 
forms the rods are simple, in other forms they anasto- 
mose to form a delicate, open mesh. The outer wall is 
often coated, obscuring the pores. 
Dictyocyathus annularis, N.Sp. Plate XL, Fig. 55. 
Small tubular form; intervallum co-efficient 5 mm., 2 
mm. Outer wall pores are obscured in the type 
specimen, but a second specimen (Fig. 55E) shows smail 
irregular pores, 3 or 4 to 1 mm. The short connecting 
rods in the intervallum tend to anastomose into hori- 
zontal rings Ca and D). The inner wall has small 
circular pores, 3 or 4 to 1 mm (Cb). A is a transverse, 
B a longitudinal view of the type specimen. C and D 
are the same further enlarged. 
Dictyocyathus irregularis (Taylor). 
In Plate XI., Fig. 56, is shown a specimen which is 
no doubt this species. ` The outer wall is coated with 
a desposit which, from its horizontal striae, appears to 
be definitely organic; it is an extreme example of the 
coating which so often obscures the outer wall pores of 
the Spirocyathina. ; 
Dictyocyathus fragilis, N.Sp. Plate XI.. Fig. 57. 
The species resembles the foregoing. It shows a 
similar striated coating to the outer wall. The inter- - 
vallum network is more open and delicate, and the inner 
wall is more openly porous than that of D. irregularis. 
The general form is a cylinder with external corruga- 
tions instead of being conical like the preceding species. 
Two specimens have been found. 
Dictyocyathus robustus, N.Sp. Plate XII., Fig. 58. 
Gently tapering cone; intervallum co-officient 2 mm.: 
6 mm. Outer wall coated with circular striae (Fig. 
58, D). Connecting rods numerous, simple and hori- 
zontal in the lower 13 mm. of the specimen; just at the 
top of the specimen vertical and horizontal connecting 
bars begin to appear Aa and C). The inner wall is 
strong and rugged, the pores near the top of the specimen 
being nearly 1 mm. in diameter and 2 mm. apart. A, B, 
longitudinal section; C,, transverse section of upper 
part; D, surface view at upper part. Only one specimen 
has been found. 
Dictyocyathus quadruplex, N.Sp. Plate XIT., Figs. 59. 60. 
The type specimen is a fragment of an expanding 
cone; intervallum co-efficient 3 mm.; 15 mm. The outer 
wall is mostly lost and what little is left is obscured and 
no pores are visible. Just under the wall the ends of the 
intervallar rods form a fairly regularly quadrate pat- 
tern; these merge into a delicate, open mesh. The inner 
wall is lighter and more openly porous than that of 
D. robustus, 
