530 PROFESSOR GREGORY ON 
by the marginal puncta. Still it resembles a Tryblionella about as much as it 
does a Nitzschia, and I therefore give it with a query as to the genus. 
103. Nitzschia distans, n. sp. Pl. XIV., figs. 103 and 1036. Form of F.V. 
nearly rectangular ; margin punctate, the puncta being very distant, some in 
pairs, others single, 5 or 6 in 0-001". The punctate margin bends slightly in- 
wards to each end, so that the ends would be narrower than the middle but for 
two small hyaline expansions at each end, which renders the extremities a very 
little broader than the middle. Length about 0:0058’; breadth about 0-001’. 
S.V. linear-lanceolate or rhombic-linear, narrow, broadest in the middle, where 
the breadth is 0:0005”; ends acute, keel central. The whole form is somewhat 
hyaline. 
This species is not rare in the Glenshira Sand, and I was only prevented from 
figuring it in my last paper on that deposit by want of room for the figure. Since 
then I have found it frequent both in Lamlash Bay and in the remarkable stony 
dredging from Loch Fine, so often mentioned, from which the present figure is 
taken. It is probably striated, but I have not been able to resolve the striation. 
I may here state that the form, of which a drawing was made, but not in- 
serted in the plate just alluded to, seems to differ in some points from this, which 
is the more frequent. In that form, the puncta, though distant, were regular, 
and, as stated in the description, which was printed without the figure, appeared 
to be constricted, and to have fine lines proceeding from one constricted punctum 
to the constriction in the next. As the F.V. of this form had not the terminal 
expansions, a circumstance which at the time I attributed to accident, I am in- 
clined to believe that that figure really represented a different species. This I 
have not had time to ascertain. But the present figure represents accurately the 
form which from the first I had named Wiz. distans. 
104. Nitzschia hyalina, n. sp. Pl. XIV., figs. 104 and 1045. Form of F-.V. 
rectangular, with expansions at the extremities. On each margin is a row of 
small puncta. Length 0-0034’; breadth 0:0004’. S.V. linear, narow, and towards 
both ends contracted to long and still narrower terminations. Keel apparently 
double ; but perhaps one is seen through the very hyaline valve. The whole form 
is so hyaline as to be easily overlooked. 
This delicate species is tolerably frequent in the Loch Fine dredging so often 
mentioned. It is possible that it may be a Homeocladia, but I have no means at 
present of deciding this point. It is certainly not one of the species of /. figured 
in the Synopsis. 
105. Pleurosigma (?) reversum,n. sp. Pl. XIV., figs. 105 and 105 6. Form 
linear-lanceolate, narrow, somewhat contracted on each side of the middle por- 
tion, and again expanding towards the ends, which are elongated, and have the 
expansion all on one side, but on opposite sides at the two apices. On the non- 
expanded side of the elongated ends, the margin is nearly straight, or slightly in- 
