Nevadia ovalis McMenamin, 1987

Gapp, Wesley, Lieberman, Bruce S., Pope, Michael C. & Dilliard, Kelly A., 2011, New olenelline trilobites from the Northwest Territories, Canada, and the phylogenetic placement of Judomia absita Fritz, 1973, Zootaxa 2918, pp. 15-28 : 23

? Nevadia ovalis McMenamin, 1987

(Fig. 6.3, 6.5, 6.6)

? Nevadia ovalis MCMENAMIN, 1987, p. 744, figs. 5.2, 5.5, 5.6, 6.1, 6.3, 6.4, 6.6.

Material examined. PWNHC-2009.20.22 and KUMIP-320712-320713 from Nevadella zone, Early Cambrian, Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada (Section 1, 199.5– 300 m above base of formation and in float).

Discussion. These specimens may be referable to Nevadia ovalis McMenamin 1987 originally described from the middle shaley interval of unit 3 of the Puerto Blanco Formation of Sonora, Mexico. For instance, the material from the Sekwi Formation appears to match that species in possessing the anterior and posterior cephalic borders much wider than in other species of Nevadia , and the extraocular area much narrower, as well as a cephalon that has an ovate shape along its anterolateral margins. However, because neither McMenamin’s (1987) original material nor the new material from the Sekwi Formation is particularly well preserved, our assignment is considered tentative, and awaits discovery and identification of new material from each of these localities. The material from the Sekwi appears distinct from the aforementioned early ontogenetic stages of cephala Fritz (1973) referred to as Nevadia ? sp., differing principally in the outline of the cephalon.

McMenamin assigned this species to the genus Nevadia based on a character of the “anterior end of the glabella well forward of the palpebral lobes.” This species remains assigned to the “nevadiids” based on the presence of characters discussed by Lieberman (1999, 2001) such as the width (tr.) of the interocular area being approximately equal to the width of the ocular lobe at its midlength and S3 conjoined medially. This is in contrast with the monophyletic Judomiodea, which is grouped by characters such as the width (tr.) of the interocular area being equal to two to three times the width of the ocular lobe at its midlength and S3 not being conjoined medially. In addition, the thoracic pleural spines are relatively short, and although this may not be typical for all members of Nevadia and Nevadella it is known from other "nevadiids", for instance, Buenellus Blaker, 1988 .

Most olenellinid species tend to have very limited geographic ranges and are often endemic to narrowly defined areas. One of the rare exceptions is Elliptocephala logani ( Walcott 1910) , which straddles both the western and eastern parts of North America (Lieberman 1999). Therefore, Nevadia ovalis , from southwestern North America, may comprise another such exception, if it is ultimately confirmed to be present in northwestern North America.