114 
PROCEEDINGS OF SOCIETIES. 
July 24nth, 1879. 
Xanthidium Rohinsoniamim, Archer, shown from a new midland 
Irish locality. — Mr. Crowe showed examples of Xanthidium 
Hohinsonianum^ being the fourth occasion this form has as yet 
been met with ; first found by Mr. Archer in co. Armagh, 
then in co. Donegal, afterwards by Mr. Crowe at Glengarifie, and 
now in co. Kildare, this well-marked little species has not yet 
been taken out of Ireland. Although its distribution is thus 
wide in this island, it must still be accounted as very rare. The 
form is small, semicells trapezoid, the rounded angles crowned by 
a few minute spines, central elevation of the semicells bearing a 
few irregularly disposed, rather conspicuous grinules ; lower . 
margins straight, isthmus slightly elongated, constriction thus 
forming a parallel and straight division between the semicells. 
A more detailed description will be given on another occasion. 
Trichia clavata, Persoon, was exhibited by Mr. G. Pirn ; this was 
found growing on moss in an orchid basket in his sto’^e. This form 
comes under the genus Uemiarcyria of Rostofinski which differs 
from Arcyria in having the capillitium in spirals, as in Trichia, 
and from Trichia, defined by him in having the spral combined 
into a dense network similar to Arcyria. This proved to be the 
fully-developed form of the immature myxomycete shown at a 
previous meeting of the Club. It w^as abundant on the wood and 
moss for many weeks. It formed a very pretty cbject viewed 
either with a low power, so as to emblace the whole, or with a 
higher one, so as to exhibit the structure of the capilitium. 
Section of Limestone from Ogradina, Banks of the Danube, 
exhibited . — Professor Hull exhibited a thin slice of limestone 
from the banks of the Danube, near Ogradina, considered to 
be of Cretaceous age. The rock from which this was taken rises 
in massive cliffs above the left bank of that river, where it 
traverses the Eastern Carpathians. As Dr. Hull could discover 
no traces of fossils, he had hoped a thin section would probably 
(as in the case of our chalk) exhibit a foraminifera. structure, 
but this expectation had not been fulfilled, as no organic 
structures were visible under the microscope in tie sections 
exhibited. The entire field consists of small particles of calcite, 
which polarise with the usual opalescent colours, and fi. into each 
other along irregular, but generally straight margins A high 
power shows the particles of calcite to be cellular in sime cases, 
and to be traversed by cleavage planes in others. Veinsof calcite 
also occur. We must assume the absence of organic stucture to 
be due to the entire replacement of the original rock b/ foreign 
matter, but of similar composition, assuming, what is generally 
admitted, that all limestone formations are of organii origin. 
The replacement of the original organised structure by crystalline 
calcite is evidently a subsequent process of “ metamorphsm,” of 
which the specimen exhibited affords an illustration. 
