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 103 b. 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 Ntz. distans. 



104. Nitzschia hyalina, n. sp. PL XIV., figs. 104 and 104 b. Form of F.V. 

 rectangular, with expansions at the extremities. On each margin is a row of 

 small puncta. Length 00034" ; breadth 00004". 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 Homceocladia, but I have no means at 

 present of deciding this point. It is certainly not one of the species of H. figured 

 in the Synopsis. 



105. Pleurosigma (f) reversum,, n. sp. PL XIV., figs. 105 and 105 b. 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- 



