GREVILLE, ON DIATOMACE. 83 
Marine. Dredged in Loch Fine, by Professor Gregory, 
1856. Lamlash Bay, Professor Balfour, 1857. In a 
dredging made the same year, off Invercloy, in Brodick 
Bay, by the Rev. Dr. Miles; Professor Walker-Arnott. 
A very characteristic species, not to be confounded with 
any of the genus already known. It appears to be both 
local and rare, as it occurs in only two of the numerous 
Arran gatherings. 
5. Nitzschia macilenta, Greg. MSS. 
Frustule linear, slightly sigmoid, truncated; side view 
linear, slender, gradually tapering towards the acute 
extremities, keel with a single row of sub-remote puncta; 
strie very obscure; length -0150” to 0190"; breadth -0004” 
to 0007"; puncta about 8 in 001”. (Figs. 8, 9.) 
Marine. Lamlash Bay, dredged by Professor Balfour, 1857. 
A fine species, evidently allied to N. sigmoidea, but de- 
cidedly less sigmoid. The side view is very narrow. The 
puncta are separated from each other by irregular intervals, 
and are fewer than in N. sigmoidea. The striz I have not 
succeeded in resolving, nor was Professor Gregory more suc- 
cessful. It is undoubtedly a marine species, and tolerably 
frequent in one of the Lamlash gatherings. 
6. Navicula forcipata, Grev. 
Valve oval or oblong, marked by two continuous longitu- 
dinal linear blank spaces, which contract opposite the nodule, 
and then expand and converge concentrically towards the 
extremities, where they almost meet; length -0013” to 
"0030"; striz 35 im 001". (Figs. 10, 11.) 
Marine. Glenshira sand, Professor Gregory. Lamlash 
Bay, dredged by Professor Balfour. Cresswell, Northumber- 
land, Dr. Donkin. Californian guano. 
After a very careful examination of this little Diatom, I 
entirely agree with Professor Gregory in regarding it as un- 
described. The examples which fell under his observation 
were very inferior to those which I have recently obtained, 
which accounts for his bemg led to compare the form with 
Navicula pygmea. The finer specimens show that it is more 
nearly related to N. Lyra and N. spectabilis, as will be seen 
at once by consulting the figures. It must indeed be con- 
fessed that large individuals at first sight seem to approach 
very near to some small varieties of N. Lyra. Iam, however, 
satisfied that the two species are really distinct. Perhaps 
the characters most to be depended on im our new form are 
—1l. The greater number of striz, about 35 im -001”; while 
