Archer— 0/2 the Genus Tetrapedia. 
299 
Latit. 0.006 mm. usque 0.008 mm. ; familise ex quaternis cellulis ex- 
tructse latit. 0.013 mm. ; familise ex cellulis 16 is extructce latit. 0.027 
mm. usque 0.03 mm. 
Tetrapedia Crux Michaeli. P. Eeinsch. 
Oellulse in sciagraphia quadraticse, margines laterales integerrimi 
utrimque leniter emarginati ; cellulae evoiutiores (in statu divisionis) 
quadripartitse, incisurarum directio in marginum lateralium directione 
angulo semirectangulo versa. (Figs. 9 to 10). 
Cellularum (in statu divisionis) latitude 0.008 mm. usque 0.012 
mm. 
The first species {T. gothica), I have never had the good fortune to 
encounter, and would, indeed, be extremely glad to have an opportu- 
nity to examine so remarkable a unicellular growth. As is seen from the 
figure (PI. XXL), a young cell in T. gothica is compressed, quadrate, 
slightly emarginate at the middle of each lateral margin, the angles 
roanded, a slight marginal concavity between each of the four central 
emarginations and each of the four angles (figs. 1, 2) ; side-view oblong, 
concave at the middle at each side, end broadly rounded (fig. 7). By- 
aad-by, as would appear, the cell becomes more and more deeply 
incised at all the four sides, the incisions, taking origin equi-distantiy 
from the angles — that is to say, from each of the four lateral emargina- 
tions, of which, indeed, these are but the initiations — proceed in a di- 
rection perpendicular to the sides, until they almost reach the centre 
(figs. 4, 5). The cell is now cut very nearly into four quadrate quar- 
ters, but these remain still mutually attached by a narrow connecting 
g portion, and, of course, this forms a bond of union, and must maintain 
a passage of intercommunication between the cavities of the four quad- 
rate sections; this, at least, is very plainly conveyed by Reinsch's 
figure. Pari passu with the progress of these lateral and vertical in- 
cisions, a growth or increase of dimensions, so far as we can judge, 
seems to occur, and each of the four quadrate sections, when the 
incisions have progressed to this extent, appears to be about equal in 
size to the original single quadrate cell. The line of incision does not 
appear to be simply rectilineal and acute below, but it leaves a some- 
what considerable interval between the segments, and at the lower or 
inner extremity it is bluntly rounded, and higher up it ofiers a some- 
what undulate appearance, whilst the general or average breadth of 
the incision is pretty much alike throughout. This undulate outline 
is due to the circumstance that each of the four margins of the four 
segments, the two inner of each, as well as the two outer, at this stage 
possesses a minute emargination at the centre, the two new angles (or 
those at the top or outer extremity of the incisions) being rounded off 
similarly to the single old angle of each (or those forming the four angles 
of the primary quadrate cell). As in a single cell the intervals between 
the central emarginations and the angles ofi'er a slight marginal conca- 
vity ; the remaining angles of each of the four segments are, of course. 
