230 Dublin Microscopical Club. 
planes are so fully developed that the rock is exceedingly friable in 
consequence. 
With a two-inch objective and the aid of the polariscope the paste is 
seen to be truly vitreous, as it becomes dark when the Nicol prisms 
are crossed. At the same time the quartz and felspar crystals 
polarize vividly. 
With a magnifying-power of 400-500 diameters numerous micro- 
liths appear. A few with parallel sides suggest the forms of 
apatite prisms, others are probably of pyroxenic origin ; there are 
also cellular spaces of amorphous matter. But the most noticeable ap- 
pearances are those of stellate forms, generally originating in a centre 
and shooting out sharp-pointed needles in various directions. Some- 
what similar forms are described by Rosenbusch from the obsidian 
of Greenland*, and by Allport from the pitchstone of Arran in 
Scotlandf. These latter differ from those observed by the author 
in the fact that they polarize distinctly, and are considered by Mr, 
Allport to be forms of pyroxene. Those in Prof. Hull’s section, 
however, do not polarize{, but with crossed Nicols entirely disap- 
pear from view along with the vitreous ‘paste of the section. These 
forms, together with the absence of polarization, suggested that in 
the present instance they are those of shrinkage fissures originating 
in various centres during the cooling process, not those of crystalline 
bodies. 
A new Sarcodine, possibly to be referred to the Genus Microgromia. 
—Mr. Archer showed examples of a very minute monothalamous 
freshwater Rhizopod, not very uncommon in moor-pools, but yet 
not hitherto recorded. Owing, however, to the fact that never yet 
was he able to alight on even a single example exhibiting pseudo- 
podia, he was actually unable to refer this form definitely to a par- 
ticular genus out of, say, three, to some one of which it might @ 
priori belong. These were Nebela, Hyalosphema, or Wicrogromia ; 
Mr. Archer, however, for the present at least, felt inclined to sup- 
pose that in the last it would most probably find its most fitting 
location. The test in this form is very minute, membranous, as it 
were, somewhat crumpled, balloon-shaped or pyriform, with a com- 
paratively thick neck, its circular opening with a distinctly marked, 
slightly thickened rim; the test, when young, colourless, but 
brownish eventually ; the body-mass granular and faintly bluish in 
tint, though it might be called “colourless,” and with a posterior 
nucleus. Were such a form as this to be seen to project even a 
single, ever so short, sharply bounded, pellucid, “finger-like” 
pseudopodium, it would doubtless fall under Nebela (Difflugia in 
part); but if so, it would be by far the most minute form known 
referable thereto; or its hyaline test might suggest Myalosphenia. 
Its very small size alone would suggest Microgromia; but still the 
larger examples are, by comparison, a good deal larger, and with a 
* Mikrosk. Phys. Band i. + Geol. Mag, vol, ix. 
t This fact was witnessed by several members of the Club present. 
In one instance the light appeared through the sides of the needle. 
