Galbagnostus galba

Galbagnostus Temporal range: Floian to Darriwillian PreЄ Є O S D C P T J K Pg N
a drawing of cephalon and pygidium of Galbagnostus galba
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Order:	Agnostida
Family:	Metagnostidae
Genus:	Galbagnostus Whittington, 1965
species
G. galba (Billings, 1865) (Type), synonym Agnostus galba G. nericiensis Ahlberg, 1992 G. valmyensis (Ross, 1958), synonym Trinodus valmyensis

Galbagnostus is an extinct genus of agnostid trilobite. It lived during the Lower and Middle Ordovician (Floian to Darriwillian).

Like all Agnostida, G. galba is diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. As in all Agnostina, G. galba has two thorax segments. When Agnostina are enroled, a tiny opening between the cephalon and the thorax becomes visible (the cephalothoracic aperture) that uniquely distinguishes this group from the Eodiscina. A feature shared with all Agnostoidea is that the frontal lobe of the central raised area of the cephalon (or glabella) is not laterally expanded compared to the backward lobe, like in the Condylopygoidea. In G. galba the glabella is short and broad. The furrow that usually separates the anterior and posterior glabella (F3) is effaced. The lateral furrows of the posterior glabella (F2) are weakly impressed. The node on the glabella is located near its anterior margin. The pygidial axis is very short, and tapers to the back. The posterior lobe is transverse trapeziform, and carries an indistinct median ridge, and behind which the axial furrow deepens.