88 WALKER-ARNOTT, ON RHABDONEMA. 
Diatomacez,’ to peruse what he says, otherwise my present 
observations may not be understood. It will be also neces- 
sary to bear in mind that, in some other genera, as Achnanthes, 
where there is a dissimilarity between the two valves of the 
frustule, the one next the point of attachment is termed the 
inferior valve, the other the superior. These terms I shall 
have occasion to employ. 
Having received lately from Professor Harvey, of Dublin, 
some Algze of the group called Corallinacee, from New 
Zealand, I washed these thoroughly, in case of any diatoms 
being mixed with the sand and mud that accumulate about 
such, and obtained a few only; but two interesting and 
closely allied forms presented themselves, along with several 
of Kutzing’s species of Grammatophora, &c. Both had a 
resemblance to what I have found m the coarse or sandy 
portions of Ichaboe guano (imported about two years ago), 
and of which I distributed some slides under the fanciful 
but only provisional name of Gephyria, as I had not then 
sufficient materials to clear up its affinities. Of the two 
from New Zealand, one exhibited a side view which some- 
what resembled a species of Swrirella ; the second was elliptic- 
linear (as if one had compressed a ring), and apparently 
pierced with numerous pentagonal holes in a double row. 
These markings sometimes extended to the end of the valve, 
sometimes stopped half way from the middle. There were 
also two forms of front views, which it was difficult to con- 
nect with the side view peculiar to it. 
On afterwards examining the Corallines, I detected a small 
specimen of Ballia callitricha, and creeping on Corallina offici- 
nalis a little piece of Polyzonia Harveyana; on both of these 
I observed a diatom which resembled closely the genus Rhab- 
donema, but of which the thread was composed of not more 
than three frustules ; this, however, might have arisen from the 
remainder being broken off, although my present impression 
is that such an appearance was not accidental. From the 
scantiness of the materials I succeeded in obtaiming only a 
very small preparation of each; and although I kept them 
separate, still, in consequence of the previous washing along 
with the Corallines, a few frustules in both instances had 
been deposited on, or caught by the Alga, on which the 
other was parasitical. At first, then, I had some doubts if 
these two were distinct, as, in both, the valves were furnished 
with coste; but the front views exhibited a different ap- 
pearance, from the septa in the one being rudimentary, 
while in the other those nearest the valves were marked 
similarly to these, and scarcely distinguishable from them. 
