ROPER, ON BRITISH MARINE DIATOMACESA. 17 
rates four modes in which sporangia are formed. The third 
is thus defined : 
“The valves of a single frustule separate, the contents set 
free, rapidly increase in bulk, and finally become condensed 
into a single Sporangium.” 
As far as regards the Melosira varians, the only one in 
. this group which I have had an opportunity of noticimg, I 
believe the process is essentially the same as in the examples 
already described. The only difference is, that the new- 
formed cell being inflated, and much larger than the original 
frustule, the valves of the frustule must necessarily be either 
ruptured or pushed apart by the increasing growth of the 
sporangium, and the latter alternative happens. 
I have seen no specimen of Mr. Brightwell’s Chetoceros 
Wighamii, but from his figures I believe the goniothecia- 
like bodies constitute another example of the formation of 
internal cells. 
I have said that I consider these internal cells sporangia, 
and essentially of the same nature as the inflated ones of 
Melosira varians. At the same time we should not forget 
that Mr. Thwaites discovered the Himantidium pectinale in a 
truly conjugated state, and that it is contrary to our experi- 
ence of the economy of nature that the same result should 
be obtained in the same species in two different ways. 
Notes on some New Spectres and Varieties of Britisn 
Marine Diatomacez. By F.C.S. Rorrr, F.L.S., F.G:S. 
Tue greater part of the British fresh-water species of 
Diatomaceze, from the facility with which they are obtained, 
and the frequent opportunities for collecting them offered to 
every observer with a microscope, have probably been already 
described; but that this is not the case with the marine spe- 
cies, is shown by the great additions lately made to this class 
by the researches of Dr. Gregory, Mr. Brightwell, and others ; 
and, as they appear to have been hitherto somewhat neglected 
on our Southern coasts, I hope to draw more particular at- 
tention to this abundant field of origimal observation by 
pointing out the best means of obtaining the marine species, 
and at the same time propose to describe a few of the more 
