77 
Plumatella casmiana, Oka. 
1907. Oka, Annot. Zool. Japon. Vi, p. 122, fig. 3. 
This species does not appear to have been recorded hitherto from 
any other country but Japan. It is, however, possible that it may have 
been confused with some other form in Europe. 
The shape of the statoblasts is quite distinctive. They are extremely 
elongate; their outline is а regulär oval; they have а very narrow swim- 
ring of uniform width and projecting very little if at all beyond the edge 
of the capsule, the free surface of which is minutely tuberculate. The 
colonies are small and entirely recumbent. The zooecia have а strongly 
tectiform outline in vertical section and are flattened below; the proximal 
part of each is somewhat faintly pigmented and has an olivaceous or 
brownish tint, wbile the distal part is colourless but not altogether hyaline. 
Branching is profuse but always in one plane. It results in the production 
of а dendritic figure in which there is no (or only а very short) main 
trunk, but а number of large primary branches can be distinguished the 
twigs of which remain fairly distinct from those of other branches. 
In the Collection from the Jeruslan river there are several small colo¬ 
nies of this species, all on fragments of the leaf of some water-plant 
Three of them are in close proximity to а colony of P. auricomis. The 
largest, which is apparently circular, has а diameter of abont 15 mm. Free 
statoblasts are abundant in the zooecia. They are very uniform in shape 
and size and closely resemble the one figured by Oka. The following are 
their average measurements: 
Length of statoblast... 0. 363 mm. 
Breadth of statoblast . .. 0. 17 mm. 
Breadth of swim-ring.. 0. 048 mm. 
In the original specimens from Japan, the statoblasts were from 0. 37 
to 0. 38 mm. long and from 0. 17 to 0. 18 mm. broad. The proportion 
of breadth to length (approximately 1: 2. 12. and 1: 2. 14) is therefore 
very similar in the two countries. 
In two of the Russian colonies the valves of the free statoblast from 
which each originated still adhere to them. The growth of the colony evi- 
dently proceeds at first for а short distance in one direction; then а bi- 
furcation takes place, and then branching becomes vigorous in different 
directions. One of the colonies bears а remarkable resemblance to а young 
colony of P. fungosa figured by Braem (op. cit. (1890) pl. ii, fig. 20). 
The large number of statoblast present proves, however, that itwasmature* 
Plumatella punctata, Hancock. 
1850. Plumatella punctata, Hancock, Ann. Nat. Hist. (2) V, p. 200, 
pl. iii, fig. 1, pl. V, figs. 6, 7. 
1857. Plumatella punctata, Allman, op. cit., p. 100, fig. 15. 
