NEW FORMS OF MARINE DIATOMACE.E. 495 



S.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. PI. 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 00005" 

 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 striae. 

 S.V. obtusely rhombic, broad, with a raphe in the median line. Striae 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. PI. X., figs. 35, 35 b, 35 c, and 35 d. 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 costae. Costae 18 or 20 in 0001". 



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. PI. X., figs. 36 and 36 b. 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 costse. Terminal nodules large and conspicuous. No central nodule. 

 Costae 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 



