PROCEEDINGS OF SOCIETIES, 273 
mixed with other forms, of Closteriwm Pritchardianum (Arch.), 
which species had presented itself copiously in one of the warm 
tanks in the Botanic Garden, watered from the River Tolka. 
Read, the following extract from a letter from Professor 
Hodges, of Belfast, dated 27th April, 1866, accompanying a 
sample of the material alluded to therein : 
“Some time ago I received a specimen of the enclosed substance 
for analysis; and on submitting it to the microscope I was sur- 
rised to find that it consisted almost entirely of Diatomacee. 
The person who forwarded it to me stated that it appeared on the 
surface of a lake near Seaforde, Co. Down, in May, 1865, and 
covered about 500 square yards, forming a layer three or four 
inches in thickness, having been driven by the wind into a sort of 
estuary. The smell was so intolerable that the people were 
obliged frequently to leave off work in the adjoining fields. I 
found it to consist, in the 100 parts, of— 
PUES eo Ae a ec ee 87°50 
Organic matters, ».:.0. 20.20.08... 10°30 
Inorganic matters ............... 2°20 
100°00 
“The mineral matters were chiefly oxide of iron and silica. 
You will find the substance very rich in Diatoms.” 
Mr. O’ Meara had carefully examined a sample of this very bad- 
smelling stuff, and had found the following Diatoms :—Oyclotella 
operculata, Synedra radians, S. capitatum, SN. delicatissima, Cocco- 
nema lanceolatum, C. parvum, OC. cymbiforme, Navicula crypto- 
cephala, Diatoma elongatum, Tabellaria flocculosa, Fragillaria capu- 
cina, Epithemia Argus, E. gibba, Cocconeis placentula, Plewrosigma 
attenuatum, P. Spenceru, Himantidium bidens, Nitzschia parvula, 
Gomphonema constrictum. Also a few sponge-spicules; and he 
suggested that Spongilla might have had something to do in pro- 
ducing the very bad odour proceeding from this curious deposit. 
Mr. Archer exhibited a number of fresh examples of the zygo- 
spores of some Desmidiacez, which, so far as he was aware, had 
rot yet been met with. 
Amongst these novelties was the zygospore of Xanthidium 
fasciculatum. Of this he showed the only two specimens he had 
ever seen; for, although the plant itself seems to be pretty com- 
mon in suitable localities, he had never before met it conjugated, 
nor did he think the zygospore was recorded. It is orbicular, 
large, beset with very long slender spines, broadest at the base, 
and tapering in a concave manner upwards (Eddystone Light- 
house like) to the bifid apices. This formed an extremely pretty 
object. 
edie: that of this fine species, and in the same gathering, he 
was able to show, not yet recorded, the zygospore of Xanthidium 
aculeatum. It, too, is large, und beset with spines, at the base 
