NEW FORMS OF MARINE DIATOMACE.E. 



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 Ehrenberg or 

 KiiTziNG ; that of Professor Smith 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. 



45. Coscinodiscus nitidus, n. sp., G. 



46. ... punctulatus, n. sp., G. 



47. ... concavus, Elir., G. 



48. ... umbonatus, n. sp. 



49. ... centralis, Ehr., G. 



50. Eupodiscus subtilis, Ralfs, n. sp. 



51. Campylodiscus centralis, n. sp. 



52. ... Ralfsii (?) Sm. 



53. ... angularis, n. sp. 



54. ... eximius, n. sp. 



55. ... limbatus, Breb. 



44. Melosira or Coscinodiscus (?) (?), n. sp. PI. 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, n. sp. PL X., fig. 45. Diameter of disc 0-0012" to 

 0-0025". Margin entire, transversely striated. Striae 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- 



