Holmiella taurus, Gapp, I. Wesley & Lieberman, Bruce S., 2014

Gapp, I. Wesley & Lieberman, Bruce S., 2014, New olenelloid trilobites from the Northwest Territories, Canada, Zootaxa 3866 (4), pp. 479-498 : 489

Holmiella taurus sp. nov.

Fig. 6

Type material. Holotype KUMIP 355545. Paratypes KUMIP 355546–355547 and PWNHC 2013.23.21–22.

Etymology. The name taurus was chosen because the large genal spines resemble the horns of a bull.

Diagnosis. Anterior constriction of cephalic border between intergenal spine and genal spine, where border meets genal spine; strongly incised S3; short ocular lobes (terminate opposite S1); anterior most part of genal spine is anterior of LA; anterior cephalic margin is approximately parallel to a sagittal line; the posterolateral margin of LA is constricted to subparallel anteriorly.

Description. Anterior cephalic margin relatively straight, extending to genal spines, parallel to the transverse line, developed as a flattened ledge; anterior cephalic border directly anterior of LA length approximately equal to length L3 and expands greatly abaxially; genal spine where attached subparallel to transverse line and then further abaxially deflected back strongly, directed slightly inward, posterior of the posterior cephalic border; length (sag.) of LA approximately equal to combined length (sag.) of L1, L2, and L3; anterior margin of LA semicircular in shape; lateral margins of LA abaxial of lateral margins of LO; anterior margin of ocular lobe separated from LA by a furrow; S3 convex anteriorly; lateral margin of L3 convex abaxially; length (sag.) of L3 equal to length of L2; S2 convex anteriorly; lateral margin of L2 convex abaxially; S1 convex anteriorly; length (sag.) of L1 is approximately 1.5 times the length of L2; lateral margins of L1 adaxial of lateral margins of LO; length (sag.) of LO is approximately length (sag.) L2 and L3; small occipital spine present; small intergenal spines present on posterior border angled abaxially.

Discussion. This species differs from numerous other species of Holmiella by various characters such as the anterior cephalic margin being nearly parallel to a transverse line, short ocular lobes that terminate posteriorly at S1, and the posterolateral margin of LA being constricted to subparallel to a sagittal line. The cephalic border between the intergenal spine and genal spine constricts anteriorly, similarly to H. falx . Like H. domackae sp. nov., the genal spines are prominently directed posteriorly, however the ends of the genal spines in H. taurus are directed more adaxially. Intergenal and occipital spines are present as they are in other species from the Sekwi Formation ( H. domackae included), which is not the case for species recovered from Nevada ( Hollingsworth, 2006).

Occurrence. Early Cambrian, Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada, Section 14, in float. Given that this material occurs in float it was impossible to determine whether it came from the Dyeran or underlying Montezuman stages (or Olenellus or Nevadella stages, respectively).

Figures

FIGURE 6. Holmiella taurus sp. nov. 1, holotype KUMIP 355545, x 1.4; 2, PWNHC 2013.23. 21 (latex cast), x 2.1; 3, KUMIP 355546, x 1.7; 4, PWNHC- 2013.23.22, x 0.9.