Vietnamia, Kobayashi, 1960

Lee, Dong-Chan, 2013, Late Ordovician trilobites from the Xiazhen Formation in Zhuzhai, Jiangxi Province, China, Acta Palaeontologica Polonica 58 (4), pp. 855-882 : 874

Vietnamia ? sp.

Fig. 8O.

Material.—One incomplete cephalon (repository number NIGP−152030).

Remarks.—The morphology of L 1, intermediate lobe, course of facial suture of this species resemble those of Calymenesun tingi ( Sun, 1931) (see Lu 1975: pl. 46: 13; Peng et al. 2000: text−fig. 1 A). This species has a longer (exsag.) palpebral lobe and wider (tr.) preglabellar area. It cannot be confirmed whether it has a pre−cranidial spine as does Calymenesun . It is the rostral plate that evidently differentiates this species from Calymenesun . The rostral plate is wide (tr.) and strongly arched dorsally (Fig. 8 O 1), whereas that of Calymenesun (see Peng et al. 2000: text−fig. 1 B – E) is much smaller and not arched dorsally. In addition, the rostral plate is located more anteriorly and dorsally than that of Calymenesun which is entirely ventral. With regard to the morphology and position, the rostral plate of this species is similar to that of Neseuretus (see Hammann 1983: pl. 4: 39b; Rabano 1990: pl. 14: 6, pl. 15: 2, 10) and Calymene (see Chatterton and Ludvigsen 2004: pl. 54: 1–4).

Compared to Vietnamia sp. A (compare Fig. 8 O 2 and Q 3), this species has a more flattened cephalon, and more strongly laterally inflated L 1. The rostral plate morphology is much different. Vietnamia sp. A has a doublure sector that is wider (tr.) than border sector; Calymene (see Chatterton and Ludvigsen 2004: pl. 54: 4) and Flexicalymene (see Evitt and Whittington 1953: pl. 9: 4–6) whose overall morphology of rostral plate is similar to this species, have a doublure sector that is narrower (tr.) than border sector. Such mixture of characters prevents the author from confidently placing this species in any of the above−mentioned genera, but the glabellar configuration leads to questionably associate it with Vietnamia .