an 
simple structure, with outer wall and inner wall (the 
latter a normally-porous structure) connected by a 
simple system of rods or trabecular mesh; this spitz is 
usually a pointed structure carrying on the general con- 
tour of the more or less conical organism. In the 
Spirocyathina there appears to be clear evidence of septa 
being formed indirectly and phylogenetically by the 
thickening and flattening of the sides of a trabecular 
lattice—an entirely different mode of origin from the 
direct formation met with in Archaeocyathina. The 
order Metacyathina shows still another mode of origin 
of septa; whereas in Spirocyathina the septal develop- 
ment is phylogenetic and is traceable by the comparative 
study of a series of species; in Metacyathina the 
development is ontogenetic, septa forming in the upper 
part of a cup of which the base has no septa or central 
cavity or inner wall, but is filled with an irregular, 
trabecular and disseptimental mass of tissue; the base 
of Metacyathina is not a sharp conical spitz, but an 
irregular mass. The majority of the septate forms of 
the Spirocyathina are characterised by synapticulae, and 
even those which no longer show synapticulae appear 
to be derived from synapticulate forms. Synapticulae 
seldom occur in the Metacyathina; on the other hand, a 
characteristic feature is the frequent presence, especially 
in the base, of “dissepiments,” irregular curved plates 
which are not for the most part porous. The distinction 
is not absolute, because Metafungia has a few dissepi- 
ments as well as numerous synapticulae, and Metaldetes 
spiralis has a few synapticulae. Dissepiments are also 
occasionally seen in Archaeocyathina in repair tissue at 
the site of an old injury or fracture: their presence here 
and in the irregular base of Metacyathina rather indicates 
their being of the nature of proliferating embryonic 
tissue. Whatever may be the relationship of Meta- 
cyathina to Archaeocyathina on the one hand, and to 
Spirocyathina on the other, and whether they be 
ultimately considered worthy of ordinal rank or not, the 
more typical genera (e.g. Metacyathus and Metaldetes) 
form a very characteristic group, and the same may be 
said of Metacoscinus. There are also some other 
abnormal Coscinocyathus-like forms which may be 
placed. provisionally in this order. The independent 
origin of septa in Spirocyathina seems almost certain, 
and so is the origin of tabula-like structures in 
Metacoscinus; the independent origin in Archaeocyathus 
trachealis has also been observed and will be referred to 
- in our next memoir. There is therefore ground for 
considering that radial septa may have arisen indepen- 
dently at least three times, and tabulae or tabula-like 
structures perhaps five times within the class. Much 
remains to be done to clear up the affinities of the 
Metacyathina, but it is clear that Bornemann's theory that 
Protopharetra is the vegetative stage of more regular 
forms, though not of general applicability, is true in 
certain limited cases. 
New Family ARCHAEOPHARETRIDAE. Plate XVII., 
Fig. 75. 
These are small irregular forms which may perhaps 
represent the primilive form of the Metacyathina, cor- 
responding to Monocyathus fox the Archaeocyathina and 
Dictyocyathus for the Spirocyathina. We have only 
found one genus and species so far, Archaeopharetra 
tpyica. 
New Genus ARCHAEOPHARETRA. 
Small irregular tubular organisms, the space within 
the outer wall filled with a mass of irregular trabecular 
and dissepimental tissue without central cavity or defined 
inner wall. Genotype: Archaecopharetra ty pica. 
Archaeopharetra typica, N.Sp. Plate XVII., Fig. 75. 
The type specimen is an irregularly corrugated tube 
3 to 4 mm. diameter and 14 mm. long. The outer wall 
is coated with silica and pores are not visible; the tissue 
within is an irregular mass of rods and dissepimental 
plates, without any definite differentiation of septa, inner 
wall or central cavity. 
Family METACYATHIDAE (Bedford). 
See Part I, page 5, plates IV., V., Figs. 26, 28 to 3l. 
The genus Metafungia is now removed to the new 
order Spirocyathina and the genus Metacoscinus to a 
new family (see below). The family now contains the 
genera Metaldetes and Metacyathus and a new genus 
Paracyathus. 
New Genus PARACYATHUS. Plate XVIL, Fig. 76. 
Small conical forms in which the base is, filled with 
irregular trabecular tissue without inner wall or septa, 
the outer wall having small irregular pores; within a 
short distance of the base clearly defined radial septa, 
inner wall and central cavity appear, and the small 
irregular outer wall pores are replaced by large and 
regular pores. 
Paracyathus parvus, N.Sp. 
Genotype of Paracyathus. It is a small cone, expand- 
ing above, shown natural size in Fig. 76 a. Intervallum 
co-efficient in upper part about 3 mm.: 9 mm.: with 
fairly stout and regular septa nearly 1 mm. apart. The 
ouler wall has a single row of large pores to each 
intersept. The base has the structure given in the generic 
description; at d, Fig. 76 C a striated coating obscures 
the pores. [t is a difficult little form to place as the 
nature of the wall pores differs greatly from those of 
Metacyathus and Metaldetes. Only one fragment has 
been found. 
