Archer — On the Genus Tetrapedia. 
301 
that even at a comparatively early period of the progress of growth of 
this form, that is, in examples with only four primary incisions, a 
foramen or aperture — an indubitable hole (''Loch") — exists right through 
and through the cell at the very centre of the common point of union 
of the segments, or in a sixteen-segmented tablet five such holes may 
present themselves. These foramina are square, or rather the sides of 
the short tube thus formed are somewhat convex inwardly, and thus 
the angles acute. In one of Reinsch's figures (fig. 5) this opening is de- 
lineated with its angles towards the ends of the incisions, and in another 
(of a sixteen-segmented tablet, fig. 6), the sides of the opening are shown 
as towards the ends of the incisions (the author does not himself refer 
to this difi'erence). To judge from Reinsch's figures, these holes seem 
very remarkable ; they are not holes in one side of the cell- wall, which, 
as we know, can sometimes occur, as in cells of Sphagnum-leaf, the 
openings in the oogonia of (Edogonium, &c., &c,, but they are holes, 
bored as it were, clean through both walls, the membrane from both sides 
lining them, thus making a free passage through the thickness of the cell. 
They are not, if we judge Reinsch's figure aright, comparable to the 
openings in the " coenobium" of a Coelastrum, or a Pediastrum, or of 
Gonium, &c., which are the spaces between the component individualized 
cells of a stratum, but here it would appear that even the tablet, 
shown in fig. 6, is still only one cell, with sixteen compartments, nearly, 
but not quite, shut off from one another, and therefore still in mutual 
intercommunication. Repeatedly vertically quadripartite is thus the 
main feature of this form. 
One of Reinsch's figures seems to ofi'er a deviation from the general 
description here sought to be conveyed (fig. 8). Pour apparently 
distinct cells are closely juxtaposed, the individual cells (instead of 
quadrate, the angles rectangular, bat, as mentioned, rounded off), are 
here equally four-lobed, the lobes semicircular and entire. Thus, 
between the four lobes occur four sinuses, these acute -angled at the 
deepest point. In the centre, between the whole four cells, there 
occurs an acutely-quadrangular hollow-sided vacant interval of equiva- 
lent length and breadth, and between each pair of the four-lobed cells 
also an acutely-quadrangular hollow-sided vacant interval, longer than 
broad, the longer diameter of these four interspaces running in the direc- 
tion of the angles of the equally quadrate central vacant interval — the 
form and direction of these {five) interspaces being, of course, simply due 
to the semicircular outlines of the lobes of the juxtaposed cells. One 
can, in fact, exactly reproduce the outline presented by the form in 
question, and even bring out the whole of the characteristics of the 
contour of fig. 8, by placing sixteen similar coins in four groups of 
four each, the coins so much overlapping one another as to allow, as 
nearly as possible, just one half the circumference of each to remain 
uncovered. Of this form Reinsch has seen but a single specimen, and, 
referring to it as he does only in the description of the plate, is disposed 
to take it for a distinct plant. 
Such (with this aberrant, or more likely quite distinct form) is this 
