NEW FORMS OF MARINE DIATOMACES. 499 
0:0005” to 0:0015". Disc cellulate; cells largest in the centre, becoming regularly 
smaller towards the margin, arranged in quincunx, but, from the diminishing 
size of the cells, in curve lines. It often happens that the cells in the two inner 
thirds of the disc are conspicuously seen, inclosed within an equilateral triangle, 
formed by three slightly curved lines of cells, beyond which the cells and lines of 
cells are so small and hyaline, as to become obscure. Such discs are convex, and 
seen on the convex side. Others, especially the largest, are much flatter, and, 
when properly focussed, exhibit the whole cellular structure plainly. 
This species is very frequent, even abundant, in Professor ALLMAN’S dredging 
from Lamlash Bay; and it is found more or less frequently in all the others. 
Possibly the disc is identical with the Coscinodiscus minor of EurenBERG or 
Korzine ; that of Professor Suiru being a fresh-water form. But the present 
species is unquestionably an Orthosira, notwithstanding the resemblance of the 
disc to Coscinodiscus. 
GROUP IV. 
Discs, INCLUDING CAMPYLODISCI. 
The new forms belonging to this group are not, in the materials examined, 
very numerous, but they are very interesting, and most of them are very fine 
species. 
44, Melosira or Coscinodiscus (?) n. sp. 50. Eupodiscus subtilis, Ralfs, n. sp. 
45. Coscinodiscus nitidus, n. sp., G. 51. Campylodiscus centralis, n. sp. 
46. fee punctulatus, n. sp., G. 52. ose Ralfsii (?) Sm. 
47. Re concavus, Ehr., G. 53. aes angularis, n. sp. 
48. re umbonatus, n. sp. 54. iy eximius, n. sp. 
49. of centralis, Ehr., G. 55. me limbatus, Bréb. 
44. Melosira or Coscinodiscus (?) (?), n. sp. Pl. X., fig. 44. Diameter 
of disc 0-003’. It is marked by fine, sharp, radiate lines, which are very numer- 
ous. These lines are strongest near the margin, which has the form of a broad, 
thick, raised rim, within which the valve’seems to sink and then to rise, the middle 
part being apparently somewhat convex. 
This disc occurs not very unfrequently in one of the Loch Fine dredgings, and 
more sparingly in one from Lamlash Bay. As no view of it is to be seen except 
the disc, or S.V., I have not been able to determine its genus, although the disc 
looks more like that of a filamentous form than a Coscinodiscus. 
45. Coscinodiscus nitidus, nu. sp. PI. X., fig. 45. Diameter of disc 0:0012’ to 
00025’. Margin entire, transversely striated. Strie of margin about 16 in 
0-001’, traceable to some small distance beyond the marginal band towards the 
centre. Surface of disc marked with distant and irregularly radiate lines of 
rather large, round, distant cells or granules. The rays are distinctly marked to- 
