Cyrtosymbole Richter, 1912

Feist, Raimund & Lerosey-Aubril, Rudy, 2005, The type species of Cyrtosymbole and the oldest (Famennian) cyrtosymboline trilobites, Acta Palaeontologica Polonica 50 (3), pp. 465-475 : 467

Genus Cyrtosymbole Richter, 1912

Type species: Dechenella escoti von Koenen, 1886 ; La Serre near Cabrières, Montagne Noire, France, early Famennian, Devonian .

Emended diagnosis.—Small, oculated Cyrtosymbolinae with conical glabella with subparabolic frontal lobe; lateral glabellar furrows incised; S1 bifurcated; preglabellar field extremely narrow or absent; pronounced antero−lateral cephalic border and border furrow; well defined palpebral lobe, placed towards anterior part of preoccipital glabella, close to axial furrow; postocular sutures with Ɛ− ζ straight; genal spines short; pygidium semicircular, with narrow, high axis; narrow border furrow and border, well defined axial rings and pleural furrows that extend as far as border furrow.

Differentiated from Calybole Richter and Richter, 1926 by the following features: glabella relatively longer with anterior outline largely parabolic, anterior sutures modestly divergent, α− α distant to each other, preglabellar field absent or extremely narrow (sag.), pygidial axis robust with wide posterior outline and higher number of axial rings. Differentiated from Haasia Yuan, 1988 by: glabella wider and unconstricted anterolaterally, librigenal spines present, pygidial axis longer with postaxial field absent or rather narrow (sag.), nodular sculpture.