49 
GONYOSTOMUM SEMEN DIESING. 
A Flagellate now first recorded for the British Isles. 
A. MALIN SMITH. 
On July 6th, 1929, I collected an organism at Austwick Moss, 
W. Yorks., v.c. 64, which I identify as above. It has been 
found each year since at the same place and also at Helwith 
Moss on June 9th, 1930, and May 7th, 1932. 
This organism belongs to the Chloromonadales, a group 
of highly specialised unicellular flagellate forms. Pascher 1 
records four genera of the group, one of which is colourless. 
These comprise six species, three of which belong to 
Gonyostomum. The only species of This group so far recorded 
for the British Isles is V acuolaria virescens Cienk, recorded 
twice in recent years < 
Gonyostomum semen is a free-swimming cell furnished with 
two flagella, one of which is directed forward and the other 
backward along a ventral groove. Two aspects of this groove 
are seen in Figs. 4 and 5. The cell is of comparatively large 
size, being 44-67 ju long and 30-36 y wide, in the examples 
measured by me. It is markedly flattened and the thickness 
is approximately three -fifths of the width, (c.f. Figs. 2 
and 3). There is no cell-wall, but the cell is bounded by a 
firm outer layer or periplast in which highly refractive 
trichocyst-like rods are embedded. These are regularly 
arranged at the anterior and posterior ends of the cell, irregu- 
larly elsewhere. (See Fig. 1). The rods at the posterior 
tip of the cell are specially noticeable, as this tip is frequently 
free from chloroplasts. The free forwardly directed flagellum 
1 ‘ Susswasserfl, Deutschlands, Osterreichs und der Schweiz.’ ii 179, 
figs. 381 and 382 (1913). 
1933 March 1 
c 
