Nileus sp.

Lee, Dong-Chan, 2013, Late Ordovician trilobites from the Xiazhen Formation in Zhuzhai, Jiangxi Province, China, Acta Palaeontologica Polonica 58 (4), pp. 855-882 : 862

Nileus sp.

Fig. 6L .

Material.—One articulated specimen minus free cheeks (repository number NIGP−152007).

Remarks.—This species resembles Nileus petilus Xia, 1978 from Hubei, China (see Zhou et al. 2005: pl. 3: 9, 15, 17, 21) and Nileus huanxianensis Zhou in Zhou et al., 1982 from Gansu, China (see Zhou and Dean 1986: pl. 60: 1–6, 8, 11) in sharing a gently curved anterior branch of facial suture and similar location of palpebral lobe. This species, however, differs in having a sagittally longer cranidial portion anterior to palpebral lobe, smaller palpebral lobe, and semi−circular pygidial outline with a slightly convex forward anterior margin. In particular, the presence of shallow anterior cranidial border and the preglabellar area that does not bend downwards indicates that this might be a new species of Nileus ; the absence of anterior cranidial border and ventrally−curving anterior cranidium are typical of Nileus (see Tjernvik 1956: pl. 2: 13 for N. limbatus Brögger, 1882 ) including N. petilus and N. huanxianensis . However, more specimens are required to officially erect it as a new species.

Figures

Fig. 6. Late Ordovician trilobites from Xiazhen Formation near Zhuzhai, Yushan County, China. A–E. Meitanillaenus? sp. A. NIGP−151995, cranidium from locality 3; dorsal (A1) and anterior (A2) views. B. NIGP−151996, cranidium from locality 3; dorsal (B1) and lateral (B2) views. C. NIGP−151997, cranidium from locality 3, dorsal view. D. NIGP−151998, cranidium from locality 3, dorsal view. E. NIGP−151999, cranidium from locality 3, dorsal view. F. Amphilichas sp., NIGP−152000, cranidium from locality 3; dorsal (F1), oblique posterior (F2), anterior (F3), and lateral (F4) views. G. Eokosovopeltis sp., NIGP−152001, pygidium from locality 2, dorsal view. H. Eokosovopeltis cf. currajongensis (Edgecombe and Webby, 2007), NIGP− 152002, pygidium from a limestone layer overlying the mudstone at locality 1, dorsal view. I. Styginidae indet. sp. B, NIGP−152003, hypostome from locality 3, ventral view. J. Styginidae indet. sp. A, NIGP−152004, incomplete thoraco−pygidium with four thoracic segments from locality 3, dorsal view. K, M. Asaphidae indet. K. NIGP−152005, free cheek from locality 2, dorsal view. M. NIGP−152006, pygidium from locality 3, dorsal view. L. Nileus sp., NIGP−152007, articulated specimen minus free cheeks from locality 2; posterior (L1), anterior (L2), lateral (L3), and dorsal (L4) views. Scale bars 2.5 mm, except E, F, I 1 mm; G, H, K 5 mm.