Archer— On the Genus Tetrapedia. 
297 
speak of almost the entire family of Desmidiese, such forms as those 
appertaining to the genera Polyedrium (Nag.), Scenedesmus (Meyen), 
Pediastrum (Meyen\ Ophiocytium (Nag.), Coelastrum (Nag.), Chara- 
cium (Al. Braan), Dimorphococcus (Al. Braun), &c., for examples of 
very varied and at same time seemingly characteristic outlines. 
But amongst unicellular plants belonging to the class Phycochro- 
macese, so frequently found in the same situations associated with the 
foregoing, as well as with other less prominently marked chlorophylla- 
ceous types, not until recently, so far as I am aware, has attention been 
drawn to any examples of a specially figured outline — that is, as men- 
tioned, in shape otherwise than globular, ellipsoidal or cylindrical. 
I need hardly contend, indeed, that the figure-of-8-shape," as- 
sumed by many such during the .progress of self- division, cannot be 
regarded as an exception, or as in itself special. Thus, in the genus 
Synechococcus (Nag.), for instance, the ordinary oblong subcylindrical 
cell becomes transversely constricted during growth, so as to assume a 
figure-of-8-shape but the two segments having attained their full 
size, the constriction is simultaneously carried through and through, se- 
paration ensues, and the oblong sub-cylindrical figure in each new cell 
is resumed. 
Possibly, indeed, the departure from the so frequent ellipsoidal 
type, which is shown by the cuneate or rather obovate cells of Gom- 
phosphceria aponina (Kiitzing), may, so far as it goes, indicate a certain 
amount of approach to a special figure, enhanced, too, as it might ap- 
pear to be, by the very pretty obcordate shape presented by the cells 
during division. Indeed, a doubly- obcordate figure is not unfrequently 
seen ; that is, when the division proceeding vertically from above down- 
wards, being partially advanced, is quickly succeeded by a second line 
of division setting in at right-angles to the former, also proceeding ver- 
tically from above downwards — then the shape assumed presents an 
obcordate outline on each of its four vertical aspects, and, when viewed 
from above, or somewhat obliquely, is seen to be four-lobed. A cell in 
such a progressive stage of division is thus somewhat comparable to the 
figure of a four-lobed Euonymus fruit. (This allusion, of course, is only 
to assist in conveying a conception of the shape presented). But, when 
the self-division is complete, the cuneate or obovate figure is resumed. 
Indeed, even the regular tapering off towards the lower or inner extre- 
mity of the cells may be possibly held to be but a consequence of their 
mutually approximate radial disposition, occurring, as they do, embed- 
ded in the substance of the ends of a number of radially projected 
dichotomously subdivided arms of rather firm gelatinous matter, ema- 
nating in a somewhat stellate though quite irregular manner from a 
common centre, the whole surrounded by a more or less conspicuous 
gelatinous envelope, and forming an unequally rounded globose family. 
Gomphosphseria thus would seem to form, to a certain extent, a parallel 
amongst ChroococcaceEe (Phycochromacese) to Oocardium amongst 
Palmellacese (Chlorophyllacese). 
It does not appear, then, until the genus Tetrapedia was founded 
R. I. A. PKOC— VOL. I-, SER. II., SCIENCE. 2 Q 
