FROM A DREDGING IN THE WEDDELL SEA. 
707 
In the Archaeocyathinae we are thus confronted with a large, diverse, and widely 
spread fauna, which appears suddenly at an early stage of the organic history of 
the world, which produced locally great reefs of calcareous material in the oceans of 
that date, and which became extinct as suddenly as it had appeared. 
Having merely a series of skeletons to work from, comparison can only be made 
with skeletons exhibiting similar shape and structure, and, despite the non-spicular 
nature of the skeleton, it seems more natural to group these organisms with sponges 
than with any other class of the animal kingdom. Of course it may be argued 
that the characters justify the creation of a new phylum, though, at present, such 
a course does not seem necessary. 
• While the salient points in the anatomy of the skeleton in most species are clear, 
the nomenclature of the group is far from satisfactory. It is impossible to group 
the present forms known as Archaeocyathus under Billings’ original or emended 
definition. Taylor has given a subdivision of the genus Archaeocyathus, but several 
of his divisions are quite worthy of generic rank. The only forms which can be 
included in the genus as defined by Billings are A. profundus, Billings, A. Sellicksi, 
Taylor, A. dissepimentalis, Taylor, and A. pauciseptatus described above. All 
the other species given under this generic title have no dissepimental tissue, and 
it seems as logical to place them in some new genus as to place those which have 
tabulae in the genus Coscinocyathus. It may be objected that in one case (A. 
Sellicksi) the dissepiments only occur near the base, and that it is really intermediate 
between the two types at present grouped under the name Archaeocyathus. But 
there are connecting forms between other genera, and it seems preferable to keep 
Billings’ definition for Archaeocyathus and erect a new genus to contain those 
forms which have straight septa and neither dissepiments nor tabulae. 
For this reason the genus Thalamocyathus, as defined above, has been instituted. 
Forms, therefore, with straight septa and neither tabulae nor dissepiments come 
into the genus Thalamocyathus ; those which have straight septa and well-marked 
tabulae are grouped under the name Coscinocyathus ; specimens with straight septa 
but irregular tabulae and dissepiments remain in the original genus of Billings, 
Archaeocyathus. 
In considering this flora and fauna from a geological point of view, it will be 
convenient to summarise the whole as follows : — 
Flora. 
Alga. 
Epiphyton fasciculatum, Chapman. 
,, grande, sp. nov. 
Fauna. 
Porifera. 
Tetractinellida, Hexactinellida, Heteractinellida , 
