Zooarium branching, but only at ends of segments. Straight needle-like rods about 5 mm long, slightly expanding. Subquadrangular cross-section, three sides are concave, one side is convex and somewhat wider than the others. Three sides with oval apertures, fourth side with 6–8 longitudinal striae.
Arthrostylus curtus (Ulrich)
Occurrence: Mount Hope
Reference: Dalvé, 1948
Arthrostylus tenuis (James, 1878)
Occurrence: Fulton, Economy, Southgate, McMicken
Reference: Bassler, 1906; Treatise.
Originally names Helopora tenuis, also called Arthronema tenuis. Especially abundant in Economy.