DUBLIN MICROSCOPICAL CLUB. , 411 
locentrotus armiger, A. Agass. The spines of this species are very 
like those of Hchinometra described in the Club Minutes of 
September, 1874, but may be distinguished from them by the 
radiating “spokes” of reticular tissue being united by lateral 
prolongations of similar structure in S. armiger, whereas in 
Kchinometra they are connected by aseries of solid bars, which 
are not joined to one another by any reticulation. 
Conjugated State of Stauroneis pheenicenteron, exhibited.— Mr. 
Archer showed the conjugated state of Stawroneis phenicenteron 
quite the same as previously described by him, common as the 
species is, but rarely encountered conjugated. When recent and 
the contents bright and healthy, this example, as a microscopic 
object, was an exceedingly bold and handsome one, though since 
being placed on the slide (some evenings since) it had much lost 
its beauty. 
Crystals of Olivine from Vesuvian Lava and Irish Basalt.—Prof. 
Hull exhibited thin slices of crystals of olivine from the lava of 
Vesuvius, and others from the basalt of the north of Ireland. 
The former, by the aid of polarised light, presented the charac- 
teristic rich play of colours, changing on rotating the analyser 
from crimson to sap-green, or from yellow to blue, or from grey ' 
to deep purple ; a beautiful banded structure was also sometimes 
apparent. On the other hand, the material filling the interior of 
the crystals of the basalt of the north of Ireland exhibited but a 
faint play of colours, changing from pale grey or green to brown ; 
whilst the interior of the crystals exhibited in some places a 
concretionary structure. A comparison of numerous specimens 
of olivine crystals from the Vesuvian lavas with those of the 
Irish basalts and melaphyres had induced Prof. Hull to come to 
the conclusion that in nearly all cases the interior of the olivine 
crystals of the Irish rocks had been replaced by some chloritic 
or other mineral, and that the specimens seen in these rocks are 
in reality a pseudomorph after olivine and not the original mineral 
itself, for it 1s well known that of all minerals olivine is the most 
hable to alteration. 
Sections of Stem of Lime, exhibited.—Dr. M‘Nab exhibited a 
transverse section of the stem of the lime-tree at the second 
year’s growth. ‘The stem had been hardened by alcohol before 
being cut into very thin sections; these were stained by being 
placed for twenty-four hours in Beale’s carmine solution. On 
examination with a moderate power the section showed the 
cambium layer, the cells of which were densely filled with 
protoplasm, most of them having the nuclei well developed. On 
each side of the cambium layer the new permanent tissue could 
be seen, the xylem part of the fibro-vascular bundles on the one 
side, the phléem part on the other. The three elements of the 
xylem or wood part, viz., the wood-prosenchyma, the wood-paren- 
chyma, and the wood-vessels could be seen, both in the new 
xylem and in the wood of the preceding year. The three elements 
of the phloem, the bast-parenchyma, and bast-vessels, and the 
