Birmanites Sheng, 1934

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 : 318

Birmanites Sheng, 1934

Type species. Ogygites birmanicus Reed, 1915 . ‘ Hwe Mawng Beds’ , northern Shan State, Myanmar, original designation .

Diagnosis. Lu’s (1975, p. 318–9) diagnosis is still largely appropriate. It should be modified to include the inverted U shape of the wide hypostomal fork, and to emphasise that the pygidial ring furrows are transverse, rather than chevron–shaped. Despite the thin cuticle, the terrace ridges on the pygidial doublure are particularly strong. Only the best-preserved material shows a pointed junction of the facial sutures on the midline. In most flattened material the sutures appear to run nearly marginally over their anterior course.

Discussion. Birmanites birmanicus was originally referred by Reed (1915) to the genus Ogygites Tromelin & Lebesconte, 1876 (type species Ogygia desmaresti Brongniart in Brongniart & Desmarest 1822), and we are therefore obliged to discuss both genera here. The type material of the type species of Ogygites is both distorted and incomplete, and a very detailed discussion of it by Rabáno (1989. p. 76–82) concluded with placing Ogygites ‘Incertae subfamiliae” within Asaphidae . She regarded the clarification of the identity of Ogygites as beyond resolution and recommended restricting its usage to the distorted holotype. Rabáno (1989) was unaware of a forthcoming revision of O. desmaresti from the type area of Angers by Pillet (1990), who attributed much additional material to the same species. Although it is distorted, much of it is articulated, and if Pillet is correct in attributing his material to O. desmaresti , as is likely, it is clear that the type species of Ogygites shares its principal features with both Birmanites and Nobiliasaphus . The pygidium is not seen on the type material, but several specimens figured by Pillet (e.g. 1990, pl. 15) prove the presence of numerous backwardly directed chevron-shaped ridges/furrows on the long and narrow pygidial axis that are clearly present also on the type specimens of Nobiliasaphus nobilis (Barrande) and Pamirotechites pamiricus Balashova, but not on Birmanites birmanicus or other oriental species of Birmanites . This is such an unusual character that in our view it is likely a synapomorphy of species sharing it, and constitutes the defining character of Nobiliasaphus / Ogygites . For example, Rabáno (1989) illustrated several species from Spain showing this feature, and Hammann & Leone (1997) illustrated others from Sardinia. One of Rabáno’s species, N. hammanni , has a posterior pygidial spine, which is not considered generically significant. However unsatisfactory its type material, it is likely that Ogygites is the senior name for this clade. If Birmanites is restricted to species with transverse pygidial ring furrows then some species may be better placed in Birmanites rather than Nobiliasaphus ; for example, Nobiliasaphus powysi Hughes, 1979 , from the Ordovician of the Builth Inlier, Wales. The range of Nobiliasaphus / Ogygites does not extend as far to the east (present geography) over Ordovician Gondwana as does that of Birmanites . Finally, Opsimasaphus Kielan, 1960 (type species O. jaanussoni Kielan, 1960 ) differs from Birmanites in having a relatively short (sag.) pygidium—the structure of the pygidial axis (with the exception of Chinese O. pseudodawanicus , see Turvey 2007) is similar to that of Birmanites rather than Nobiliasaphus / Ogygites , and the cephalic features seem to us identical to those of Birmanites . Kielan (1960, p. 75-77) gave a detailed account of Opsimasaphus in relation to what would now be called Nobiliasaphus Přibyl and Vaněk, 1965 , but did not bring Birmanites into the discussion, possibly because when she was writing this genus was still regarded as a dikelokephalinid. Chugaeva (1958) described Ogygites almatyensis from Kazakhstan, which would be better placed in Birmanites on the criteria given here. It is possible that Opsimasaphus is a subjective junior synonym of Birmanites , as discussed by Zhou & Dean (1986) and Romano & Owen (1993), while Opsimasaphus was retained by Turvey (2007, p. 366).