NEW FORMS OF MARINE DIATOMACEA. 495 
8.V. we might find it to be a Diadesmis, that is, a catenated species, having na- 
viculoid frustules. But I do not venture to name it on conjecture, and I only 
refer it, with the three preceding forms, to Denticula provisionally, in order that 
some name may be used in speaking of them. Indeed it is probable that the 
three preceding species may also prove to belong to Diadesmis. My present ob- 
ject is, not to determine their genus, for which I do not possess the necessary 
data, but only to point them out as well-marked species, for the researches of 
other naturalists. 
34. Denticula nana, n. sp. Pl. X., fig. 34. Form of the F.V., which occurs in 
chains of two, three, four, and occasionally more, rectangular, expanding a little 
in the middle, and also at the apices, which are truncate. Length from (:0005” 
to 0-001”; breadth, in the shorter examples, 0-0003” to 0:0004”, and less in the 
longer ones. Margin of F.V. faintly denticulate, from the ends of the striz. 
S.V. obtusely rhombic, broad, with araphe in the median line. Striz rather fine, 
inclined. 
This little form is tolerably frequent, both in Lamlash Bay and in Loch Fine. 
I think it is properly referred to Denticula, although it has some resemblance to 
some of the forms figured by foreign authors under the name of Zygoceros. 
35. Denticula minor, n. sp. Pl. X., figs. 35, 35 6, 35c, and 35d. Form of F.V., 
which occurs in chains of from two to seven or eight, on the whole rectangular; 
sometimes exactly so, more frequently with an angular expansion at the apices, 
which become capitate and subtruncate, while the margin is convex in the middle. 
Length from 0:0005” to 0-002”; breadth from 0-0002” to 0-0006”. Margins of 
F.V. strongly denticulate. S.V. rhombic or rhombic-lanceolate, very narrow, with 
srong marginal costze. Costve 18 or 20 in 0-001”. 
This form, which is very frequent in the Lamlash Bay dredgings, and also in 
one of those from Loch Fine, varies much both in size and shape, the F.V. being 
sometimes as short as the shortest D. nana, and very broad in proportion, bulging 
in the middle, and capitate, sometimes longer, rectangular, and broad ; and most 
frequently longer, much narrower, and capitate. The S.V. is so narrow, that the 
frustule seldom lies on that side, so as to present it to the eye. It appears to 
belong distinctly to Denticula. 
36. Denticula distans, n. sp. Pl. X., figs. 36 and 366. Form of F.V., which oc- 
curs in chains of from two to five or six, and also solitary, rectangular, rather broad; 
often convex on the sides, and with the ends a little expanded. Margin strongly 
denticulate. Length 0:0017” to 0:0026”; breadth 0-0006” to 0:0008”. S.V. rhom- 
bic or rhombic-lanceolate, broad; marked with very strong, distant, sharp, and 
marginal coste. Terminal nodules large and conspicuous. No central nodule. 
Costz about 10 in 0:001”. Valve thick and glassy. 
This fine species is tolerably frequent, both in Lamlash Bay and in Loch Fine. 
There is a considerable resemblance between this and the preceding species, so 
