330 PROCEEDINGS OF SOCIETIES. 
form, belonging to the verticillate spines, has the central hollow 
variable in diameter, sometimes entirely obliterated by network ; 
reticulated tissue variable in «quantity, solid pieces in the form of 
bars, dilated at the circumferance into paddle- or spade-shaped 
forms. 
Composition of Vesuvian Lava.—Prof. Hull, F.R.S., exhibited 
a thin slice of Vesuvian lava of the year 1868, remarkable for the 
large number of well-formed crystals of leucite containing fluid- 
cavities, visible with comparatively low powers. Although the 
occurrence of such fluid-cavities is not unusual, and has been 
noticed by Zirkel, Rosenbuseh, and others, yet, cut of fifteen slices 
examined under the microscope from different beds of lava poured 
forth during the last 200 years, there were none found in which 
the cavities with fluid bubbles were so numerous as this of the year 
1868. The cavities generally correspond to the angles of the erys- 
tal, which in section is an octagon, and in some cases a double row 
of cells was to be observed. ‘The crystals were set in a paste con- 
sisting of mineral glass, plagioclase, augite and titanoferrite, inti- 
mately mixed; containing along with the leucite—sodalite, mica, 
and other substances. It was assumed that each bubble of fluid 
contained in the cavities was originally in the state of steam, which 
must have been present in great quantity during the solidification 
of the lava. 
Mr. Porte remarked, some others of the meeting being disposed 
to concur with him, that the optical aspect of these little “ bubbles ” 
appeared rather that of air-bubbles than of fluid. Some experiments 
were then tried as to whether these little bubbles could be made to 
alter their position by inverting the preparations, but no such alter- 
ation seemed to take place. 
Leaves Stained and Mounted in “ Deane’s Gelatine.””—Mr. G. 
Pim showed preparations of leaves mounted as permanent speci- 
mens, which had been first bleached by nitric acid and water, equal 
parts, to which was added one drachm of chlorate of potash per 
ounce; they were then washed and stained, some in “ Dichroic 
Ink,” some in tincture of carmine, and some in a mixture of both, 
and then mounted in “ Deane’s Gelatine.”” These formed readily 
examined preparations ; by “ focussing down”? the epidermis, veins, 
and median tissue, could be successively brought into view. 
Aphis Vastator mounted twenty-five years ago exhibited —Mr. 
Robinson showed preparations of foregoing, mounted so long ago 
as twenty-five years by Topping, and in as good condition as ever. 
Colorado Beetle exhibited—Mr. Kirby showed a specimen of 
the much-talked-of and dreaded Potato-pest, the Colorado beetle ; 
he exhibited a leg of same under the microscope. 
New Species of Coscinodiscus, C. Moseleyi, O’ Meara, exhibited. — 
Rev. E. O’Meara presented a Coscinodiscus from material collected 
at Kerguelens Land, by Mr. Moseley, of H.M.S. “Challenger,” 
which he named as above. It stands in close relation to the group 
of which C. omphalis may be regarded as the type ; it is very large, 
being in diameter 0-02, and so much arched that, when the central 
