Glaucostegus Bonaparte, 1846

Last, Peter R., Séret, Bernard & Naylor, Gavin J. P., 2016, A new species of guitarfish, Rhinobatos borneensis sp. nov. with a redefinition of the family-level classification in the order Rhinopristiformes (Chondrichthyes: Batoidea), Zootaxa 4117 (4), pp. 451-475 : 472-473

Genus Glaucostegus Bonaparte, 1846

Type species. Rhina cemiculus Geoffroy St. Hilaire, 1827 (subsequent designation).

Description. Nostrils moderately elongate to very elongate and narrowly separated, length usually greatly exceeding internasal distance; posterior aperture very elongate and narrow, not or only slightly oblique to anterior aperture. Anterior nasal flaps bilobed, not fused to form a nasal curtain, inner lobe short based; inserted on snout adjacent nostril anterior margin, lateral and well anterior to innermost corner of posterior aperture (flap insertions very widely separated, by much more than internasal distance); anterior aperture very large, elongate oval, posteromedial edge formed by narrow outer lobe-like extension of anterior nasal flap (positioned medially on nostril rather than near its lateral corner); outer lobe preceded by long anterior fold; inner lobe of anterior nasal flap narrow with straight to weakly convex margin; posterior margin of anterior aperture bordered by medium-sized (almost as wide as aperture), long-based, posterolateral nasal flap; free lobe of posterolateral nasal flap extending posteromedially, but rarely reaching middle of posterior aperture of nostril; posterior nasal flap weak, width similar to posterolateral nasal flap and base short (much less than half of nostril length). Lower jaw straight or weakly undulate; skin margin forming upper lip variably concave; 3–5 short lateral grooves at its angle; oral groove weak, confined to chin.

Species. G. ce m i c u l u s (Geoffroy St. Hilaire, 1817), G. granulatus (Cuvier, 1829) , G. h a l a v i (Forsskål, 1775), G. obtusus (Müller & Henle, 1841) , G. thouin (Anonymous, 1798) , G. t y p u s (Bennett, 1830).