76 THE PHYLOGENY OF THE GENUS BRACHIOMONAS 
a few specimens which showed precise gareement with Bohlin’s 
description of B. submarina. Again a few days later, at Aale- 
sund, south of Trondhjem, I collected typical material, and here 
in great abundance. At this station some pools were almost 
exclusively filled with slender forms corresponding to Bohlin’s 
B. gracilis; in other pools a mixture of the two species, with 
perplexing intermediate forms, appeared. Observing pools con- 
taining a natural pure culture, one would scarcely question 
the distinctness of the two species: when both were found 
together in the same pool, the variety of forms seen presented a 
very strong suggestion of hybridization between the two species. 
New material collected in New York in March and April, 
1921, has furnished forms (Fics. 5-7) almost precisely like the 
slender cells illustrated by West, together with others showing 
every gradation to the broadest type of B. submarina. These 
slender forms closely resemble Bohlin’s f. rb of B. gracilis, 
but I am now convinced that West was entirely justified in 
including them in the very variable broader species. We seem 
not to have in America, and I did not find in England the ex- 
treme forms represented by Bohlin’s f. za and rc of B. gracilis. 
Whether they are sufficiently distinct to warrant the main- 
tenance of the second species is a question which would be more 
convincingly settled through studies by pure culture methods. 
I first found Brachiomonas submarina in March, 1907, in 
a small rock pool on the shore of Long Island Sound at Twin 
Island, Pelham Bay, New York. It was found in almost pure 
culture, coloring the water green from its abundance, and per- 
sisted in the motile condition for some weeks when brought to 
the laboratory. Although the same station was visited many 
times during the following twelve years, no Brachiomonas was 
found until-the middle of November, 1919, when it was again 
abundant in the same pool, and occurred sparingly in neighbor- 
ing rock hollows of similar character. I found it repeatedly 
in the same pools until the first of December, in spite of hard 
frosts and ice formation during these two weeks, The habitat 
appears to be very like that of Bohlin’s type station, small 
hollows so high above ordinary tide limits as to seem to be filled 
only with rain water, which are nevertheless sometimes dashed 
by waves so as to become brackish, as evidenced by taste and 
by the salt incrustation left on the rock margin upon evaporation. 
About the time of the collection in 1919, an unusually high tide 
was reported, and it is possible that this may have washed the 
