Pygidium with five pleural ribs. Pygidial axis up to 90% of pygidial length, very gently constrained posteriorly, with eight axial rings plus a very short terminal piece.
Pleural field gently vaulted, with five pleural ribs evenly bent posteriorly adaxially.
The available data from earlier descriptions and illustrations suggest that the pygidium of Omegops tilabadensis differs from that of Omegops accipitrinus accipitrinus in having five (not six) pleural ribs and a relatively longer axis (90% against 75%) less strongly tapering posteriorly.
Both have pygidia with 7-9 axial rings and six pleural ribs (Struve 1976), while in Omegops tilabadensis specimens with eight axial rings and five pleural ribs are invariably characteristic.
Both subspecies differ from the types of Omegops accipitrinus accipitrinus in the morphology of the visual surface with up to 46 lenses arranged in seven horizontal rows (Farsan 1998, figs 4, 5), and unlike Omegops accipitrinus (s.l.), they have a pygidium with only five (not six) pleural ribs (Farsan 1998, pl.
Anal fin origin between the pleural ribs
of vertebrae 8 in males, and the pleural ribs
of vertebrae 10 and 11 in females.
Pleurae with four, rarely five pleural ribs evenly curved backwards distally.
Pygidium transverse, trapezoidal in outline, with five faint axial rings and up to three weakly defined pleural ribs. Pygidial marginal spines short, stout; posterior margin between them gently convex, weakly tipped medially.
Pleural fields gently sloping outwards, with up to three weakly defined pairs of pleural ribs more clearly expressed on the internal moulds.
The new species differs from the type species Dactylocephalus dactyloides Hsu, 1948 in having a cranidium with the effaced glabella lacking segmentation, a shorter preglabellar field (sag.), an effaced, transverse pygidium trapezoidal in outline with axial and pleural ribs expressed mainly on the ventral side of the sclerite, and a gently convex posterior margin between marginal pygidial spines.
In the description, counts of vertebrae and pleural ribs were taken from radiographs of the holotype and two female paratypes.
Anal-fin origin at twelfth pleural ribs of vertebrae in males, and pleural ribs of vertebrae ninth in females.