FROM A DREDGING IN THE WEDDELL SEA. 
697 
The question now arises, can we separate Archaeocyatlius, Spirocyathus, and 
Protopharetra ? In the first place, it must be admitted that the greater number 
of species placed under the heading Archaeocyathus are excluded at once from 
consideration, as they contain no dissepimental tissue, the structure, which really 
causes all the complexity. It seems better to institute a new generic name for 
such simple forms, and the name Thalamocyathus has accordingly been adopted 
for such examples. In discussing the affinities of Spirocyathus and Protopharetra 
with Archaeocyathus , the particular species one has in mind is A. profundus. That 
species is described more fully by Hinde than by Billings. The outer and 
inner walls and septa are porous, the septa straight, and dissepiments oblique 
and imperforate. Spirocyathus has septa which are much corrugated, and the 
septal pores are large, a character also noticeable in Protopharetra. Dissepimental 
laminae are not nearly so common in Spirocyathus as in Protopharetra , and the 
inner wall is very distinctive, Protopharetra having several rows of pores between 
the septa, and Spirocyathus only one row. 
Thus far Protopharetra has been considered as a distinct genus. We now pass 
to consider a similar type which gradually passes into quite a different form, and 
hence partly confirms Bornemann’s view that Protopharetra was a type of rooting 
structure rather than a genus complete in itself. Such examples are taken up 
under different generic names, and Taylor’s Metaldetes is a convenient genus for 
some types. 
Metaldetes, Taylor, 1910.* 
Metaldetes plicatus, sp. nov. 
A type referable to Taylor’s genus Metaldetes is fairly common in small 
irregularly folded fragments. Complete examples seem rare, but one such is 
shown in PI. VI, fig. 68, The cup has been distinctly plicated, and it is attached 
in part to a specimen of Spirocyathus atlantic’us, which is seen in oblique longi- 
tudinal section near the top of the figure. There are certain well-marked characters 
in this new species. The septa are very numerous, straight and porous (as is in- 
dicated by the discontinuous course of the septa). The intervallum is very narrow, 
varying from 1 mm. to 1'3 mm., but where the section is oblique it seems 
much broader. Another distinct feature is the presence of numerous dissepiments, 
which, however, seem better described as irregular tabulae. They are much 
better displayed in longitudinal section (PI. VI, fig. 69), and each crosses 
several loculi. The septa show here as vertical rods, again markedly discon- 
tinuous. These discontinuities are explained by reference to PI. VI, fig. 71, a 
and b. Here an oblique longitudinal radial section of the cup crosses several 
septa, but the porous nature of these laminae is clearly indicated. The pores 
average 4 per mm. 
* Mein. Roy. Soc. South Australia, vol. ii, part ii, 1910. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART IV (NO. 27). 108 
