192 NATURAL HISTORY SOCIETY OF DUBLIN. 
_ I have, lastly, to call your attention to a curious state of the pretty 
little fern, Botrychium vulgare. This plant has the ordinary fronds, 
and fruit-bearing fronds normally separate from each other, but-in this 
case it will be seen that there are several spore-cases on the back of one 
of the divisions of the lower pinnee of the ordinary frond; thus showing 
a tendency to revert to the typical state of most species of ferns, which 
bear their fruit on the backs of the pinnules of the fronds. 
After which was read a continuation of a paper on “‘ Some New 
and Little-known Fresh-water Rhizopoda,” by William Archer. As 
certain drawings illustrative of the new forms are not yet complete, and 
some of the animals must be refound for that purpose, Mr. Archer would 
defer publishing his paper for the present, hoping to be able to do so 
in extenso in next Part of the Society’s ‘‘ Proceedings.” 
The following paper was read : — 
Norr on a PEcuLIAR Cyst-L1ke StRucTURE, ENCLOSING ExaMPLEs oF 
STAURASTRUM CUSPIDATUM (BREB.), AND OTHER MINUTE ALc@. By 
Wiritam ARCHER. | | 
I raxe the opportunity to show some sketches illustrative of a peculiar 
kind of cyst enveloping either a single or sometimes two examples of 
Staurastrum cuspidatum (Bréb.), which I have lately encountered. 
This very remarkable-looking production is usually of a definite figure, 
with yellowish-green contents, and a thick wall. Thus these two 
organisms, one inside the other, present a somewhat surprising ap- 
pearance. . 
The most usual form of the outer inclosing cell is that of a de- 
pressed or very short prism, the wall rather thick, and each of the angles 
somewhat drawn out, and thickened into a more or less prominent 
tubercle. A variety of forms of this investing cellular structure, how- 
ever, occur, such as polyhedral, semicircular, &c.; but in all instances 
the margins thickened more or less, and the angles tuberculated. Inside 
the prismatic cells, the Staurastrum mostly stands vertically ; when there 
are two individuals contained, they mostly stand one above the other 
in a direct line, then often seemingly as if just after self-division, inas- 
much as the inner segments frequently appear smaller than those above 
and below. In the triangular cysts the Staurastrum mostly stands with 
its angles directed towards the angles of the former, with usually 
but a litte space between the ends of the Staurastrum, above and below, 
and the inner surface of the cyst. Not unfrequently, however, this 
regular position is disturbed, and this especially in those external cells 
of an indefinite figure. When first taken, the contained Staurastra 
seemed to present their ordinary green appearance, but in many of the 
specimens, after being kept for a little, they became more or less brown 
and dead-looking. 
One distinct entity thus right in the middle of another—in fact com- 
pletely invested thereby, and seeming both of vegetable nature—together 
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