36 S etc hell. — An Examination of the Species 
of the pools in the neighbourhood of Cambridge about the 
first of May. By the beginning of the last week in May the 
fungus is not uncommon, and is to be found from that time on 
until the Lemnae disappear in October or November. 
Distribution. A pool known as ‘ Glacialis,’ near Cambridge, 
Mass., was the first locality, and was discovered in June, 1889. 
I have also found it in Newton, Mass. Prof. J. E. Humphrey, 
of Amherst, Mass., has kindly sent material collected by him 
at Belchertown, Mass. 
Burrillia pustulata, sp. et gen. n. 
In the present form, only very recently discovered, we 
have a species which is still another addition to the curious 
forms already described. It inhabits the leaves of Sagittaria 
variabilis , forming upon them yellow spots of circular shape 
and small size. On the under side is seen what in dried 
specimens looks like a Cystopus. The epidermis is raised in a 
small blister-like swelling which finally ruptures, when a sort 
of powdery appearance shows beneath. 
On cutting a section through an infected spot it is seen that 
the sori are situated just over the epidermis of the lower side. 
They are ellipsoidal bodies of a white or light-brown colour, 
being very different in general appearance from the brown 
sori of most of the species of the Doassansia-g roup. They 
measure from 200 /x to 350 /x by 150 /x to 180 /x. Often several 
sori have grown together into one long sorus. 
The structure is different from that of any of the other sori 
here described. The central portion is composed of paren- 
chymatous cells with watery contents and moderately thick 
walls. When the sorus is approaching maturity these cells 
have conspicuous globules of oil in them, but they lack the 
definitely globular or ellipsoidal shape of the spores, as well as 
the dense, granular, highly refractive contents. Outside of 
this mass of cells follow several layers of spores rather closely 
compacted together (Fig. 84). They are slightly polyhedral, 
4 to 6 p in diameter, and resemble in all respects the spores 
of Doassansia. There is no cortex of parenchymatous cells, 
