234 Dublin Microscopical Club. 
there is a similar form of the closely resembling Staurastrum 
O’Mearii. Such cases tend to confirm the conclusion that Arthro- 
desmus, as a genus, cannot stand; still the species relegated to 
Arthrodesmus stand, per se, very good indeed. They show that there 
is as little reason for a separate genus for two-angled Staurastra as 
for the three- or four- or five-angled, as distinguished from one 
another. 
Sections of Fetal Vertebre.—Dr. Harvey showed a section of 
foetal vertebrae stained with purpurine. All the effects for which 
double staining had been so much recommended of late, in studying 
the process of ossification in cartilage, are brought out by this dye. 
The cartilage matrix remains unstained, the new territories of bone- 
substance assume a distinct though somewhat pale hue, while all 
the cells (cartilage-cells, bone-cells, osteoblasts, and marrow-cells) 
become brilliantly stained—Mr. E. G. Hull subsequently showed a 
transverse section through the medulla of a human foetus at full 
term, at the level of the apex of the calamus scriptorius (lower apex 
of fourth ventricle), showing the nuclei of the vagus and hypoglossal 
nerves (respiratory centre). 
Tetraploa aristata exhibited—Mr. Pim showed examples of 
Tetraploa aristata from dead Pampas-grass stems in his garden. 
This is a very rare Torulaceous fungus. It appears to consist of 
about eight cells, superposed two and two; from each of the upper 
four arises a long bristle or awn, the whole forming a pretty and 
singular object. 
Structure of Micaceous Dolerite from Slieve Gullion.—Prof. Hull, 
F.R.S., exhibited a thin section of micaceous dolerite from Sleve 
Gullion, a mountain on the borders of Armagh and Louth rising 
1893 feet above the sea. The rock occurs in association with 
quartziferous porphyry, and is probably of volcanic origin, belonging 
to a period more ancient than the Miocene lavas of co. Antrim. It 
is represented on the map of the Geological Survey, sheet 59. It 
is a rock of rare occurrence, as it is seldom that mica and augite 
are associated as essentials together in the same rock. It is 
largely crystalline-granular, and of a dark colour. 
With a low magnifying-power and the aid of the polariscope the 
slice presents a very beautiful appearance, as all the minerals 
polarize more or less vividly. The following were observed :— 
1. Orthoclase, in large crystals, rare. 
2. Plagioclase, probably Labradorite, in long plates and prisms, 
perfectly crystallized, and indenting the augite. Some small crys- 
tals are seen enclosed in the latter mineral, which was consequently 
later in consolidating. 
3. Augite, in large coloured patches without erystalline form, 
indented by the crystals of felspar. 
4, Mica, easily recognizable in hand-specimens, and equally 
abundant with augite, from which it may be distinguished in the 
thin section by its parallel cleavage-planes. 
