Nileus sp.

Fortey, Richard A., Wernette, Shelly J. & Hughes, Nigel C., 2022, Revision of F. R. C. Reed’s Ordovician trilobite types from Myanmar (Burma) and western Yunnan Province, China, Zootaxa 5162 (4), pp. 301-356 : 328

Nileus sp.

Fig. 8.9

1917 Nileus armadillo Dalman; Reed, p. 49–50, pl. 8, fig. 5.

Material. Hypostome from Shihtien Formation (Darriwilian) at Pupiao, Fig. 8.9 ( Reed, 1917, pl. 8, fig. 5), GSI 11904.

Discussion. Reed (1917) correctly associated this hypostome with Nileidae , but his identification with Nileus armadillo on the basis of this sclerite alone was hardly justifiable in view of the difference in age. His identification of a second Nileus species ( Reed 1917, pl. 8, fig. 6) on the basis of a free cheek cannot be supported as the eye is too small and the anterior course of the suture wrong for this genus. Several genera of Nileidae have been added since Reed’s time, and their hypostomes are conservative, with broad lateral borders converging in a shallow embayment with a median tooth. The Burmese species has strong, relatively sparse, nearly transverse terrace ridges compared with many species. The closest match we can find is with the hypostome of Nileus symphysuroides Lu, 1957 , as illustrated by Zhou et al. (2016, pl. 52, fig. 13) from the Pagoda Limestone (Katian) and widespread in China. Without the rest of the exoskeleton the identification is cautious.

Figures

FIGURE 8. (1–6) Birmanites yunnanensis (Reed) from the Shihtien Formation (Darriwilian), Pupiao, Baoshan Prefecture, western Yunnan, China. 1. Librigena (original of Reed 1917, pl. 7, fig. 3), GSI 11892. 2. Pygidium (original of Reed 1917, pl. 7, fig. 6), GSI 11895. 3. Pygidium (original of Reed 1917, pl. 7, fig. 8), GSI 11897. 4. Librigena (original of Reed 1917, pl. 7, fig. 5), GSI 11894. 5. Articulated specimen (original of Reed 1917, pl. 6, fig. 12), GSI 11887. 6. Cephalon (original of Reed 1917, pl. 6, fig. 14), GSI 11889. (7, 10) Remopleuriidae gen. et sp. indet. (Reed) from the Shihtien Formation (Darriwilian), Pupiao, Baoshan Prefecture, western Yunnan, China. 7. Cranidium, (original of Reed 1917, pl. 6, fig. 9), GSI 11884. 10. Librigena (original of Reed 1917, pl. 6, fig. 10), GSI 11885. (8) Dolerobasilicus? sp. (Reed), Pygidium (original of Reed 1915, pl. 7, fig. 3), GSI 11535, Lower Naungkangyi Beds, Nawa, northern Shan State, Myanmar. (9) Nileus sp., Hypostome (original of Reed 1917, pl. 8, fig. 5), GSI 11904, Shihtien Formation (Darriwilian), Pupiao, Baoshan Prefecture, western Yunnan, China. (11, 12) Niobe sp. (Reed). 11a, b. Pygidium (original of Reed 1915, pl. 5, fig. 14), GSI 11516, Hwe Mawng Beds (uppermost Katian), Nati, northern part of Shan State, Myanmar, original and retrodeformation. 12. Pygidium (original of Reed 1917, pl. 6, fig. 11), GSI 11886, Shihtien Formation (Darriwilian), Shidian, Baoshan Prefecture, western Yunnan, China. Scale bars = 5 mm for 1–6, 8, 9; = 2 mm for 7, 10–12)