Transactions. 55 
The genus Didymograptus of the Moffat district, belongs to the 
upper Llandeilo black shales. I have brought several specimens 
forward to-night, which we may examine. It will be found that 
the cellules are attached to the under or inferior side of the two 
arms. It will also be seen that the spines are both on the upper 
and lower, and some cells are without any whatever. It will also 
be observed that those belonging to the Arenig, or of the Skiddaw 
and Quebec groups, have their cells on the uppermost side of the 
stipe, which is the reverse of the Moffat specimens. Locality— 
Dobb’s Linn, Hartfell, &e. 
The genus fetiolites was originally founded by Barrande, who 
described one species Ret. Geinitzianus, which he obtained from 
the upper Silurian rocks of Central Bohemia, and figured in his 
valuable memoir upon the Graptolites of that country, published 
in 1850. This genus is one of the mast interesting of those 
belonging to the Graptolitic group, but unfortunately our know- 
ledge of its structure is limited, and must, I think, remain so, 
until a more extensive collection of specimens, in a more perfect 
condition than hitherto attainable, has been formed and carefully 
studied. In its general outward appearance the genus Retiolites 
resembles those of Diplograptus and Climacograptus in having a 
central stipe or solid axis, to which is attached a double row of 
cells, giving it a rather leaf-like appearance, but widely differing 
from those forms in its internal structure. It may be mentioned 
that in the year 1873 I exhibited a specimen with remarks before 
the Geological Society of Glasgow, which I named Retiolites 
branchiatus, and which was a beautiful example of the genus, 
from the lower Graptolitic shales of Dobb’s Linn, near Moffat. 
On another occasion afterwards, in the same place, I was for- 
tunate enough in discovering a new species of Retiolites, differing 
entirely from anything I had previously got at Dobb’s Linn. It 
was found in the upper shales, showing that the genus had lived 
through the whole range of strata as represented in the Moffat 
beds. This new species I showed to Professor Lapworth on one 
of his visits to Glasgow, which he afterwards named Retiolites 
Daironi, and it is figured in Transactions of N. H. Society of 
Belfast, and this is an enlarged drawing of the same. You will 
easily perceive how widely it differs in its internal structure from 
some of the other species. The length of the fronds seem to vary 
from 3 inches to 4 inches; while their greatest breadth near the 
centre is } of an inch. They have a long, slender stipe in the 
