Illaenus Dalman, 1827

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 : 345

Illaenus Dalman, 1827

Discussion. Reed (1915, 1917) described a number of Illaenus species from both the northern part of the Shan State and western Yunnan, mostly from fragmentary material. Attempts to make casts from the illustrated specimens were variably successful, but are included here for the sake of completeness. Since the classic works of Jaanusson (1954) and Bruton & Owen (1988) it has been clear that for meaningful systematics of Illaenus species it is necessary to know such features as the dorsal surface sculpture, particularly on the cephalon, details of muscle insertion areas, and such ventral features as the outline and extent of the pygidial doublure. Reed’s specimens do not show most of these important features, and are not determinable in a modern way. Only one species, Illaenus caecoides , from Shihtien, Yunnan, was formally named. One cranidial fragment from Yunnan illustrated by Reed (1917, pl. 8, fig. 3) as Illaenus cf. tauricornis is not only incomplete, but also an internal mould, and very distorted. It is not worth re-illustrating. Two other fragmentary illaenids from Yunnan described by Reed (1917) as Illaenu s cf. oblongatus and I. aff punctulosus, were not successfully cast, and are not discussed in this paper. There is no reason to reproduce Reed’s original remarks for the illaenids and only brief comments will be given here. All except I. caecoides were recorded by Reed under open nomenclature.