260 ARCHER, ON MICRASTERIAS MAHABULESHWARENSIS. 
that it did turn up, I should never, indeed, for one moment, 
imagine that I had met with but a variety of the known 
British form. I venture to think they differ, mdeed, as 
much as two allied species need or can. To me, indeed, 
there appears a greater affinity in character of surface be- 
tween M, expansa, var. y (Wallich),* and the form in ques- 
tion, than between the latter and WM. Americana (Ehr.). In 
the two forms just pointed out the character of the margins 
of the lobes, too, is alike; but the lateral lobes m Dr. 
Wallich’s “var. y” are not bipartite, and the end lobe 
wants the vertical processes. I have, of course, never seen 
M. expansa, nor M. arcuata, nor “ var. y:”’ but I feel bound 
to say, even though it be but conjecturally, that all three 
seem to me to be abundantly distinct. 
In M. Americana the lateral lobes are short and broad, 
more or less conspicuously divided in a dichotomous manner 
by both a primary and secondary very shallow, simple in- 
cision, their sublobes short, expanding, the ultimate sub- 
divisions more or less acutely dentate; in Dr. Wallich’s 
var. 0 (M. Mahabuleshwarensis, Hobson), the lateral lobes 
are narrow, not divided in a dichotomous manner, but by a 
single deep and wide sinus, the margin serrated; the two 
sublobes produced, divergent and tapering, their extremities 
bi- or tridentate. In the former the empty frond appears 
with scattered puncta, in the latter without puncta, but with 
a marginal series of granules bordering the sinuses. 
It may be, indeed, that I may never have the pleasure to 
see an actual example of this form, but I must own, never- 
theless, that I must for the future (at least ad interim) look 
upon it in my mind’s eye as quite a different thing from 
M. Americana, and must regard it, not as “var. 6” of that 
species, but as the quite independent, yet thereto nearly re- 
lated, species, bearing the (unfortunately rather cacophonous) 
name, Micrasterias Mahabuleshwarensis (Hobson).t+ 
* «Aun, Nat. Hist.,’ 3rd ser., vol. xiii, fig. 9. 
+ Since this paper was written I have met with a paper by Professor A. 
Grunow on certain Diatomaceze and Desmidiacee from the Island Banka,! 
in which that author describes and figures a Micrasterias called by him 
Micrasterias Wallichii, which seems very closely related to the above-dilated- 
on M. Mahabuleshwarensis, but still, I believe, a distinct species; therefore 
I am pleased to find that so experienced an observer as Grunow is of the 
same opinion as myself upon that form—that is, he cannot coincide in 
the view that Wallich’s plant (— W. Mahabuleshwarensis, Hobs.) is only a 
* Grunow: “Ueber die von Herrn Gerstenberger in Rabenhorst’s 
Decaden ausgegebenen Siisswasser-Diatomaceen und Desmidiaceen von der 
Insel Banka,” &c.; in Rabenhorst’s ‘ Beitrage zur niheren Kenntniss und 
Verbreitung der Algen,’ Heft ii, 1865, p. 1. 
