214 Proceedings of Royal Society of Edinburgh. [sess, 
unlike each other. Here, again, it was only after many turnings 
over of the specimen that I was able to convince myself (especially 
after seeing it as in 1, b) that these two forms were actually within 
the intact parent frustule. The larger of the two young ones has 
a very wide girdle-zone, and is apparently distended in this 
direction to the utmost capacity of the girdle, giving it a drum- 
shape. The other, which in both figures presents the girdle-view 
(having moved within the parent), shows a girdle indeed of a 
scarcely perceptible breadth, and apparently so tightly shut up 
that the rounded ends of the diatom practically meet each other 
at the girdle, and the figure of the whole is oval rather than drum- 
shaped with convex ends. Both have numerous chromatophores, 
of the usual shape in Coscinodiscus concinnus , but arranged in stars. 
This specimen, however, interested me particularly, as showing that 
more than one so-called “ cyst ” could he produced at a time, — that 
it was not always a simple rejuvenescence of the whole cell-contents, 
that the protoplasm, in short, sometimes divided before the pro- 
duction of these bodies. 
While occupied with the study of these forms last April, I was 
much struck by the abundance in the Clyde sea area, and especially 
in Loch Fyne, of minute Coscinodisci presenting the characters of 
C. concinnus. They occurred singly, hut for the greater part in 
small packets of eight and of sixteen (Plate II. figs. 4 and 5). 
Other numbers occurred, e.g., four, hut the prevalent number was 
eight, and less frequently sixteen. I could not help observing 
that, when there were sixteen, the individuals were approximately 
half the size of those in packets of eight, and it was the like case 
with those in the packets of eight and of four (see Plate II. figs. 
4 and 5). They were held together in all cases by a fine mem- 
brane represented in the figures. The valve-view was very slightly 
convex, not nearly so much so as the parent frustule in fig. 1, b , more 
like that of fig. 2, b , hut even less so, and in the packets of eight 
the young diatoms, though larger, were considerably thinner (girdle- 
view) than those of the packets of sixteen. The instances in figs. 
4 and 5 are perhaps extreme — hut there was considerable variety in 
the respects mentioned, and yet the packets were all unmistakably 
of like origin. 
While the source of these packets remained a mystery, I took, on 
