On Two New Members of the Volvocacese. 131 
Pyramimonas delicatulus, sp. n. 
A small motile organism, which has been found to belong to 
the Polyblepharidece, occurred in abundance in the autumn of 1908. 
It belongs to the genus Pyramimonas, Schmarda (1850), 1 and is the 
first member of the sub-family Polyblepharidece to be recorded for 
the British Isles. 
Collections of algae from various parts of the pool have been 
made every alternate week since October 17th, 1908. Pyramimonas 
was first noticed on November 14th, 1908. It occurred sparingly 
among Elodea and various species of Potamogeton, but abundantly 
in the soft mud of the shallower parts of the pool. The temperature 
of the w r ater at this date was 8 , 5 n C. 2 The alga became more 
plentiful up to December 12th, when the temperature had steadily 
and uniformly gone down to 3’4"C. At the end of December, the 
temperature suddenly sank to P3 n C and the alga became less 
abundant. The low temperature was maintained during the 
beginning of January, 1909, and by the middle of the month the alga 
had almost entirely disappeared. At the beginning of February, 
1909, the temperature rose to 6'5"C., and the organism became more 
plentiful again. No specimen was found in any instance in 
collections obtained from the surface water. 
Pyramimonas delicatulus moves at considerable speed through 
the water. It appears to swing from side to side as it moves, 
its motion resembling rather the Flagellate than the Chlamydomonad 
type. Its four cilia are strong and thick. They do not taper, but 
appear to end abruptly, and can easily be seen without any staining. 
When the organism is at rest the cilia lie back over the body of 
the cell. When under observation the alga very often comes to 
rest with its ciliated end downwards, and never the other way. 3 
This position may be assumed owing to the attempts of the 
organism to travel towards the bright light. It is stopped by the 
glass slide and comes to rest in the position observed. 
The chloroplast is cup-shaped, with the sides deeply cleft into 
four lobes, each of which has a small incision at the extremity. 
The incision is not visible except in the anterior axial view (Fig. 
1 Consult Dill. Jahrbiicher fiir wiss. Botanik, Heft. 3, Band 
XXVIII., 1895, pp. 351-353; also Blochmann, Die Mikros- 
kopische Thierwelt des Siisswassers, Abt. I., Protozoa, 1895. 
p. 62. 
2 All temperatures were surface temperatures taken at a depth 
of 4 to 6 inches. 
3 Consult Dill, loc. cit., plate figure 46. This shows P. tetrarhyncus 
in the exact position that P. delicatulus assumes. 
