NEW FORMS OF MARINE DIATOMACES. 479 
certain extent on the F.V., but most towards the extremities, indicating that the 
S.V. is more convex near the ends than in the middle. I have named this form 
from its resemblance to a small two-headed club. 
It occurs only in one of the Loch Fine dredgings, in which, though far from 
frequent, I have been able to examine many more specimens than are required to 
ascertain the characters of the dead form. I observe that it often occurs in pairs, 
as well as solitary, so that it may perhaps belong to a filamentous genus, such as 
Diadesmis. But as I cannot be sure of this, without seeing the living or growing 
form, I refer it, for the present, to Navicula. 
6. Navicula Musca, n. sp. Pl. IX., fig.6. Form of valve deeply constricted in 
the middle, broadest at a point near the middle on each side of it, and almost 
triangular thence to the acute apices. Length 0-002’; greatest breadth 0:0011” ; 
breadth at middle 0:00075”. Striation confined to a marginal band, which is 
rather broad, and nearly of uniform width, except at the apices. Median line 
sharp; central nodule definite. Strize coarse, 18 in 0-001”; distant, moniliform. 
Aspect of the valve transparent. 
The form of this very pretty species is allied to that of V. didyma and the other 
panduriform Naviculze, which are so frequent in marine gatherings. Even its form, 
however, is peculiar, and it is at once distinguished from all the others by its mar- 
ginal striation. It so much resembles in shape the body of a bee or wasp, that L 
should have named it Apis or Vespa, had not these names been already appro- 
priated to other species by EdrENBERG. I have chosen, therefore, the specific name 
Musca, as the form is also that of various large flies. It occurs in the same Loch 
Fine gathering, as Nos. 1, 3, and 5; a gathering which, though very scanty and very 
stony, has proved singularly rich in undescribed forms, especially of Amphorze, 
as we shall see farther on. This dredging was a very coarse sand, which, after 
boiling with acid, I was on the point of rejecting as useless, when I observed a 
very trifling cloud of finer matter. This, though full of mica, supplied a remark- 
able proportion of new species; so much so, that I believe it contained as many 
of these as of known species; and of the undescribed forms found in it, a majo- 
rity have occurred in it alone. I mention these facts, in order to show that every 
dredging, however unpromising, in such localities as Loch Fine and the Clyde, 
ought to be closely examined. This one was most unpromising; yet it turned 
out not only rich in new species, but very different from the other dredgings made 
in the same waters. 
7. Navicula rectangulata,n.sp. Pl. IX., fig. 7. Form of 8.V. rectangular, the 
extremities being rounded; rather narrow. Length from 0003” to 0:004’; 
breadth about 0:0006" to 0:0008”. Striation highly radiate, there being three 
centres of radiation on each side—one in the middle, and one at each end. Strize 
soft, not very fine, subdistant; about 22 in 0-001", not quite reaching the median 
