Article: Revision of the Silurian graptolite genus Retiolites

The three Retiolites species, R. geinitzianus, R. australis and R. angustidens, may be distinguished only by differences in their dorso-ventral width (both the maximum attained and the rate of increase from the proximal end). Other characters used previously in specific discrimination are septal bar inclination and meshwork density. The former shows considerable intraspecific variation, with no consistent differences between the species. The latter is dependent upon the astogenetic stage of the specimen examined. Whilst R, geinitzianus and R. angustidens appear to have been of very widespread distribution, specimens of R. australis are known only from north of the Silurian equator. All three species have long stratigraphical ranges (for graptoloids) and are thus of little biostratigraphical utility other than in indicating a Telychian (Upper Llandovery) or Wenlock age.