NEW FORMS OF MARINE DIATOMACE.E. 487 



Smithii (olim N elliptica Sm.), because I have always understood the typical N. 

 Smithii to be a form which is very frequent in the Glenshira sand, and occurs also 

 in the new materials. It is of a short, broad, inelegant, oval shape, flat, colourless, 

 and much less coarsely striated. Neither does it exhibit the longitudinal ridge so 

 distinctly. It may be, that the present form, N.fusca, is the typical one, and the 

 other a variety of it ; but in my experience I have only seen N. fusca in the 

 gatherings above named, while I observe N. Smithii in every marine gathering. 



16. Navicula Smithii, var. 7, nitescens. PI. I., fig. 16. Form lanceolate, tend- 

 ing to rhombic, with obtuse ends. Median line straight, nodule definite. Length 

 from 0-002" to 0-0035"; breadth from 00009"' to 0014". Striae about 16 in 

 0-001", considerably inclined, obscurely moniliform, and of a shining aspect. 

 They are traversed by a ridge, which is about half-way from the margin to the 

 median line, and has an outline more rhombic than that of the valve. 



This form occurs both in Lamlash Bay and in Loch Fine, and is not at all 

 rare in some of the dredgings. It is conspicuous, from its elegant form and shin- 

 ing aspect. It is quite colourless under a low power. I have given it as a variety 

 of N. Smithii, from a desire to avoid unnecessary multiplication of species. But I 

 am inclined to regard it as distinct from that species, from its peculiar form, its 

 smaller size, the character of the nodule and median line, and its bright white 

 aspect ; all of which characters are very constant. 



17. Navicula Smithii, var. 3, suborbicularis. PL IX., fig. 17. Form a short, 

 broad oval, or suborbicular. Length 0-002" to 0-0026"; breadth 0-0013" to 

 0-0018". Median line bounded by white lines, curving inwards both to the apices 

 and to the indefinite nodule. Striation conspicuous, much inclined. Striae 16 or 18 

 in 0-001", moniliform. There is a ridge, as in the two preceding forms, traversing 

 the striae, and when the striae near the margin are in focus, those between the 

 ridge and the median line are very faint. 



This form occurs in Lamlash Bay, and is also tolerably frequent in one Loch 

 Fine gathering, in which the preceding form is not found. Its small size, nearly 

 round form, and peculiar median line, with the slightly-marked ridge, compared 

 to that in the two preceding forms, seem to point it out as distinct ; especially as 

 it is very constant in its characters. But, for the reasons already stated, I give 

 it as a variety. It is at least a form to be noticed, and to be considered with the 

 others with a view to a more accurate determination of species than has yet been 

 possible, but which, in the progress of observation, we may hope to attain. 



18. Navicula maxima, Greg. PL IX., figs. 18, and 18 b. Form of S.V. linear, 

 rather narrow, with obtuse ends. Length from 0002" to 0-008" ; breadth of S.V. 

 from 000025" to 0-00011"; of F.V. in the larger specimens, 0-0009" in the middle, 

 0001 15" at the ends. Striae fine, but distinct, about 52 in 0-091", parallel, not 

 quite reaching the median line, from which, at the centre, they retire, leaving a 

 pretty large round space. F.V. rectangular but narrowest at the middle, and 



