balanolobus is derived from the Greek 'balanos', acorn, and 'lobos', lobe, in reference to the outline of the rear lobe of the rhachis.
sidenbladhi has been named in honor of the Swedish philosopher and paleontologist :sv:Elis Sidenbladh|Elis Sidenbladh.
waldorfstatleri is named after the muppets Statler and Waldorf for the likeness of the rhachis to their heads.
Taxonomy
Geragnostus is very similar to Trinodus and may in future be included in that genus. In Trinodus the posterior lobe of the pygidial axis is clearly shorter than the anterior and middle lobes combined, while in Geragnostus it is equal or greater in length. Geragnostus is not closely related to Micragnostus, because its glabella is structurally different.
G. splendens, was excavated from the Lower and Middle Ordovician of Baltica and the Czech Republic
G. waldorfstatleri, has been found in the Lower and Middle Ordovician of South China
Unidentified species in the genus Geragnostus have among others been found in Colombia.
Description
Like all Agnostida, Geragnostus is diminutive, with the headshield and tailshield of approximately the same size and outline. Like all Agnostina, Geragnostus has only two thorax segments, where known. The cephalon is subquadrate in outline, and almost as long as wide. The highest point is the node in the centre of the centrally raised section of the cephalon. The glabella is about times the length of the cephalon, and its sides are very gently tapered forward, with a broadly rounded front, and is well defined by shallow furrows and an abrupt change in exoskeletal slope. It is 2 times as long as wide. The elongated glabellar node is prominent. The rear of the glabella is straight. Just in front of the node, a depression curves forward- and outward. The basal lobes are wider than they are long and almost touch. The border is relatively narrow, gently convex, and defined by a wide, shallow border furrow, widest at the front. The genal angles are pointed without spines. The pygidial axis is – times as long as the pygidium, almost parallel-sided, very slightly constricted at the middle lobe, broadly rounded, and – times as long as wide. It has three distinct pairs of lobes, and is defined by shallow furrows. The forward lobe of the rhachis is a bit shorter and wider than the middle lobe and separated from it by a furrow which is directed outward and slightly backward from the dorsal furrow, and then curved strongly forward adaxially. The rear lobe is – longer than both others together, and the furrow is directed outward and slightly forward from the dorsal furrow. The middle lobe has a prominent tubercle, which extends backwards above the anterior portion of rear lobe. It is the highest point of the pygidium. The border is moderately wide, gently convex, defined by a shallow furrow, and widest at the rear corners which carry a pair of strong, backwardly directed spines.
