Vol 5 - Dumfriesshire & Galloway Natural History and Antiquarian ...

—TransartionR. 55The genus Didymograptus of the Moffat district, belongs to tlieupper Llandeilo black shales. I have brought several specimensforward to-night, which we may examine.It will be found thatthe cellules are attached to the under or inferior side of the twoarms. It will also be seen that tlie spines are both on the upperand lower, and some cells are without any whatever.It will alsobe observed that those belonging to the Arenig, or of the Skiddawand Quebec groups, have their cells on the uppermost side of thestipe, which is the reverse of the Moffat specimens. LocalityDobb's Linn, Hartfell, &c.The genus Retiolites was originally founded by Barrande, whodescribed one species Ret.Geinitzianus, which he obtained fromthe upper Silurian rocks of Central Bohemia, and figured in liisvaluable memoir upon the Graptolites of that country, publishedin 1850. This genus is one of the most interesting of thosebeloiiging to the Graptolitic group, but unfortunately our knowledgeof its structure is limited, and must, I think, remain so^until a more extensive collection of specimens, in a more perfectcondition tlian hitherto attainable, has been formed and carefullystudied.In its general outward appearance the genus Retiolitesreseml)les those of Diplograptiis and Cliniacograptus in having acentral stipe or solid axis, to which isattached a double row ofcells, giving it a rather leaf-like appearance, but widely differingfrom those forms in its internal structure.It may be mentionedthat in the year 1873 I exhibited a specimen with remarks beforethe Geological Society of Glasgow, which I named Retiolitesbranchiatus, and which was a beautiful example of the genus,from the lower Graptolitic shales of Dobb's Linn, near Moffat.On anotlier occasion afterwards, in the same place, I was fortunateenough in discovering a new species of Retiolites, differingentirely from anything I had previously got at Dobb's Linn. Itwas found in the upper shales, showing that the genus had livedthrough the whole range of strata as represented in the Moffatbeds. This new species I showed to Professor Lapworth on oneof his visits to Glasgow, which he afterwards named RetiolitesDaironi, and it is figured in Transactions of N. H. Society ofBelfast, and this is an enlai'ged drawing of the same. You willeasily perceive how widely it differs in its internal structure fromsome of the other species.The length of the fi'onds seem to varyfrom 3 inches to 4 inches ; while tlieir greatest breadth near thecentre is \ of an inch. They have a long, slender stipe in the