Diatomella balfouriana

DIATOMELLA, nob. Frustules quadrangular (forming at first a plano-compressed filament, at length separating) . Coloured vittæ two, straight, interrupted in the middle and at each end. Length •0004'' to •0010". Diatomella Balfouriana. Pl. IX. fig. 10-13. Grannmatophora ? Βalfouriana, W. Sm. MSS. The general characters of this minute species are visible with¬out difficulty under a magnifying power of 400 or 500 diameters. The frustule is surrounded by a thickened border, and is divided into three more or less equal parts by two straight internal septa or bars not clearly defined externally, on each of which, at about equal distances between the middle and ends, are situated two dark-coloured short vittæ, while at the ends themselves the septa terminate in minute nodules. In the most elongated frustules the coloured vittæ are linear, but they contract in proportion as the frustules diminish in length, until they lose the character of vittæ and resemble nodules. The middle portion of the frustule is blank, while the spaces between the septa and the margin are transversely striated, but it requires a power of at least 600 diameters to bring this character out. The frustules of this diatom are not unfrequently seen in the process of self-division, and one of these I have represented in the plate. It will be perceived that a narrow separation has already taken place, and that in each portion the lateral striae are apparent, while as yet there is only one septum. The next stage in the process would probably be the division of the single septum into two, followed by the development of the blank middle space.

• Author
  Grev. 1855