Article: Silurian Girvanella from the Welsh Borderland
Hazel M. Johnson
A general survey of the calcareous algae from Silurian limestones of the Welsh Border has yielded many algal remains particularly of the genus Girvanella. Nine species of this genus are here described, eight of which are new; and they are grouped according to their size and mode of growth. The Sarmenta group includes three new species, G. sarmenta, G. fragila, and G. prolixa; the Problematica group two new species, G. pusilla, G. incompta as well as G. problematica and its var. lumbricalis; the Media group with one new species G. media, and the Ramosa group two new species G. ramosa and G. effusa. The basis for subdividing the genus is given and the distribution of the specific forms in the varied lithology of the limestones are recorded.