Ser. RuoposperMEx. Fam. Corallinee ? 
Puate CLXVI. 
LITHOCYSTIS ALLMANNI, Zar. 
Gen. Cuar. “ Plant calcareous, consisting of a single plane of cellules, 
which are disposed in radiating dichotomous series forming an ap- 
pressed flabelliform frond.” Ad/m.  Lirnocystis (Ad/m.),— from 
Aibos, a stone, and xvors, a bladder; because the cells are coated with 
a stony membrane. 
Lituocystis A//manni. 
Has. Parasitical on Chrysymenia clavellosa, from an Oyster-bed, Malahide, 
Dublin Bay, Professor Ad/man. 
Geoar. Distr. ? 
Descr. “This minute Alga presents itself to the naked eye in the form of very 
small whitish dots scattered over the surface of the vegetable, which it has 
selected for its parasitic growth. Under the microscope each dot is seen to 
consist sometimes of one, but more frequently of a cluster of several 
transparent and colourless flabelliform fronds, whose component cellules 
radiate from the apex of the frond, and after repeated dichotomous division, 
terminate by forming a convex margin. In almost all the cells there may 
be seen a very evident spherical nucleus. The whole plant is brittle, and 
pulverisable under pressure, its hyaline frond being mainly composed of 
carbonate of lime, which does not merely incrust it, but is intimately 
incorporated with its tissues. In Lithocystis, indeed, the carbonate of lime 
would seem in every way to represent and replace the silica of the Diato- 
macee. Under the action of dilute acid the mineral matter is entirely 
dissolved, and nothing remains but an exceedingly delicate organic film, in 
which the original form of the plant can with difficulty be detected. Nothing 
distinctly referable to fruetification has been seen in any of the specimens 
examined. Lithocystis manifestly approximates very closely to Coleochete, 
a genus established by Brebisson for a fresh-water Alga, and one with 
which the Phylactidium of Kiitzimg is evidently identical. Setting aside 
the sheathed bristles of Coleochete—a character by no means constant— 
Lithocystis would appear to differ from the latter chiefly by its calcareous 
composition, a feature, however, of much importance, and plainly bringing 
the present plant into direct relation with the Corallines.” Ad/m. 
a ee 
In one of the best books of the last generation written for the 
amusement and instruction of young persons,—I mean Hvenings 
at Home,—there is an excellent paper, headed “Eyes and no 
yes, or the Art of Seemg.” The history of the discovery of the 
curious and beautiful little plant here figured reminds me of that 
paper, offering, as it does, a striking illustration of the advantage 
to a naturalist of having his eye constantly on the watch. My 
