Published online by Cambridge University Press: 01 May 2009
As the result of examining a considerable number of specimens belonging to the species Monograptus fimbriatus, M. raitzhainiensis, and M. triangulatus from certain strata of Llandovery age at a locality in North Cardiganshire, the writer is led to the conclusion that the forms comprised within these species constitute a continuously graded morphological series; and that the stratigraphical occurrence of these forms shows that this series is, further, an evolutionary lineage.