Lochmanolenellus cf. primus

Webster, Mark & Bohach, Lisa L., 2014, Systematic revision of the trilobite genera Laudonia and Lochmanolenellus (Olenelloidea) from the lower Dyeran (Cambrian Series 2) of western Laurentia, Zootaxa 3824 (1), pp. 1-66 : 33-34

Lochmanolenellus cf. primus 2

Fig. 10.4–10.7

Material. One cephalon from GSC locality 95189 ( GSC 137491), and three cephala from GSC locality 95190 ( GSC 137488 to GSC 137490).

Occurrence. CANADA: Cassiar Mountains, British Columbia: GSC locality 95189, limestone approximately10.6 metres above the base of Unit 4 of the Rosella Formation; and GSC locality 95190, limestone approximately12.5 metres above the base of Unit 4 of the Rosella Formation; both in Section 2 of Fritz (1978, textfig. 3.1a), on the north bank of the Dease River, approximately 2.7 kilometres (1.7 miles) east of McDame.

Discussion. Four poorly preserved cephala from the Cassiar Mountains are possibly conspecific with Lochmanolenellus primus . The smallest cephalon is in phase 3 of cephalic development (Fig. 10.4; sagittal cephalic length estimated to be approximately 1.77 mm), and the other three are earliest to mid-phase 5 (Fig. 10.5–10.7; sagittal cephalic lengths estimated to be approximately 2.6 mm, 5.7 mm, and 6.8 mm, respectively). All are therefore smaller than the holotype of the species. Most of their differences from the holotype are consistent with ontogenetic trends known to occur within other species of the genus: when arranged by size, these specimens document (1) a progressive anterior migration of the genal spine base from a position transversely opposite the lateral margin of L2 to a position transversely opposite the lateral margin of L3; (2) a progressive rotation of the distal portion of the posterior cephalic margin into a more directly anteriorly oriented direction; (3) a proportional shortening of the ocular lobe such that the posterior tip migrates from a position transversely opposite the posterior half of the lateral margin of L1 to a position transversely opposite the anterior half of the lateral margin of L1; and (4) a proportional widening (tr.) of the cephalon, especially in the posterior portion of the extraocular area and the proximal portion of the posterior cephalic margin. The specimens potentially differ from Lo. primus in possessing a more arcuate (convex posteriorly) proximal portion of the posterior cephalic margin, such that the intergenal spine base is slightly more anteriorly located (Fig. 10.6), and in possessing a distal portion of the posterior cephalic margin that is slightly more strongly anteriorly oriented than might be expected for their size (Fig. 10.6, 10.7). Until such differences can be unambiguously resolved as representing either intraspecific variation or interspecific disparity, the Canadian specimens are conservatively left in open nomenclature and treated as Lo. cf. primus 2—this name also emphasizes that the Canadian material might not represent the same species as Lo. cf. primus 1 from Mexico.