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 I'everse of the Moffat specimens. Locality — 

 Dobb's Linn, Hartfell, <kc. 



The genus Retiolites 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 most 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 tlian hitherto attainable, has been formed and carefully 

 studied. In its general outward appearance the genus Retiolites 

 resembles those of Diplograptns 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 (.Jlasgow, 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 anytliing I had previously got at Dobb's Linn. It 

 was found in the upper shales, showing tliat 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 



