Redescription of Holmia inusitata (Trilobita) from the Lower Cambrian of Scandinavia
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Well-preserved topotype material of Holmia inusitata Ahlberg and Bergstrom, in Ahlberg et at., from the Lower Cambrian of Lauselva, southern Norway, allows a redescription of the species. Intraspecific variation of characters, such as the expansion and relative length (sagittal) of the anterior glabellar lobe and the curvature and length of the ocular lobes, is shown. The species is, however, considered a typical member of Holmia. A discussion of character variation and distribution within species of Holmia further demonstrates a great degree of intrageneric variation. Thus, the newly erected Baltobergstroemia Lieberman is regarded as a subjective synonym of Holmia, since the differences between the two genera can only effectively be applied to the type species. The age of the succession with H. inusitata is not well constrained by regional lithological correlations or by an acritarch assemblage, and lacks the well-differentiated faunas of the uppermost zones in the Lower Cambrian of Scandinavia. It is obvious that it must be older than the Holmia kjerulfi-group Zone, and strata with H. inusitata are, therefore, maintained as a discrete zone underlying that zone.