386 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
same frustule. (9) Marginal or intra-marginal circlets of spines are a 
very variable character. (10) The rosette in the centre of C. radialus , 
&c., is not a mark of species. (11) Craspedodiscus is not generieally 
or specifically distinct from Coscinodiscus. (12) The occurrence of two 
thin places in the rim of Coscinodiscus is not a mark of species. (13) 
Confluence of alveoli into larger ones is not a mark of generic difference. 
Much further knowledge is required of the life-history of diatoms before 
we can lay down final laws as to the limitation of genera and species. 
New Genera of Diatoms. — M. P. T. Cleve* describes a new genus 
of Diatomaceae, Dictyoneis, including several new species, and others 
previously included under Navicula, Pseudodiploneis, and Mastogloia , in 
which the outer layer of the valve is composed of large areolations, 
having the form of vesicles, and giving to this layer a reticulated 
appearance. It is exclusively marine, and from the warmer parts of 
the globe ; fossil forms are also known. 
Brunia is a new fossil genus from Japan, described by M. M. J. 
Tempere,j' in which the valve has the form of a round plate, the hollow 
of which is moderately deep, and has its walls at right angles to the 
bottom ; the edge is beautifully sculptured. 
Diatoms from Java.t — Among a collection of freshwater diatoms 
from Java, Herr O. Muller describes one in both the fresh and fossil 
condition, which must have persisted unchanged since the Middle 
Tertiaries, Melosira undulata. It is remarkable from the fact that 
many individuals have more than one stalk ; and apparently any spot in 
the cell-wall can give rise to a stalk which connects itself with any 
spot in a neighbouring cell. The stalk appears to be a product of 
transformation of the outermost layer of the cell- wall. The author 
also had under his observation a fragment of a fossil auxospore, and 
was able to determine that the mode of formation of auxospores was 
the same in those remote times as to-day. 
Pearls of Pleurosigma angulatum.§ — Regarding the controversy 
whether the so-called “ pearls ” of this diatom are round or hexagonal, 
M. L. Duchesne states that it is shown by photomicrometrical observa- 
tion that their apparent form is simply a question of focusing. If the 
objective is focused exactly to the summits of the pearls, they appear 
round, if to their base or lower, a hexagonal image is obtained. The 
author’s own observations lead him to the conclusion that their true 
shape is round. 
Commenting on this paper, Dr. J. Pelletan || maintains, contrary to 
the view of Van Ileurck, that the “ pearls ” are not hexagonal and 
hollow, but are really, as their name implies, hemispherical projecting 
grains, which may possibly become hexagonal at their base owing to 
reciprocal pressure. When the focal plane was tangent to the pearls, 
each pearl was represented by a black spot (the top which was in focus) 
surrounded by a white circle (the rest of the pearl which was not in 
focus). As the focal plane was lowered, each pearl gave a larger and 
* Le Diatomiste, i. (1890) pp. 14-7. t T. c., pp. 21-2 (1 pi.). 
X Ber. Deutsch. Bot. Gesell., viii. (1890) pp. 318-31 (1 pi.). 
§ Le Diatomiste, i. (1890) pp. 27-30 (2 pis.). 
|1 Journ. de Micrographie, v. (IS91) p. 356. 
