. Bulletin. Natural history; Natuurlijke historie. 20 Peabody Museum Bulletin 45. Figure 4. 1. Olenellus robsonensis (Burling), ?Upper Mahto Fm., drift block on the slope of the Mural glacier below Mumm Peak, near Mount Robson, British Columbia, Canada, GSC 5272, holotype, furrow is not visible at the anterior margin of the ocular lobe; and in O. roddyi the extraoc- ular area is gently convex, whereas in O. transitans it is prominently flattened. In addition to these qualitative characters, there exist quantitative character differ- ences between these taxa that allow them to be discrimi
. Bulletin. Natural history; Natuurlijke historie. 20 Peabody Museum Bulletin 45. Figure 4. 1. Olenellus robsonensis (Burling), ?Upper Mahto Fm., drift block on the slope of the Mural glacier below Mumm Peak, near Mount Robson, British Columbia, Canada, GSC 5272, holotype, furrow is not visible at the anterior margin of the ocular lobe; and in O. roddyi the extraoc- ular area is gently convex, whereas in O. transitans it is prominently flattened. In addition to these qualitative characters, there exist quantitative character differ- ences between these taxa that allow them to be discriminated at a high level of statistical sig- nificance. One such quantitative character difference is the ratio of the length (sag.) of the preglabellar area relative to the length (sag.) of L4. The following ratios for these variables were calculated for all adequately preserved and available specimens of O. transitans (, , , , , ) and O. roddyi (, , , , , , , , , , , , , , ). The mean value of this ratio in O. transitans is ±, whereas the mean value of this ratio in O. roddyi is ±, and these values differ significantly (p< by the two sample t-test, Minitab 1995 v. lOXtra [1995]). The median values of this ratio in O. transitans () and O. roddyi () differ (p< by Mann Whitney u-test, Minitab 1995 v. lOXtra [1995]). Thus, on the basis of these character differences, these two species are treated as distinct, although they are as- sumed to be very closely related. Material examined: AMNH 24214 (3 specimens), 24215 (2 specimens), 24256, 24263 (4. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Peabody Museum of Natural History. New Haven : The Museum
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