Protovirgularia McCoy, 1850

Emended  diagnosis : Horizontal or subhorizontal cylindri­cal trace fossil, trapezoidal, almond or triangular in crosssection, distinctly or in distinctly bilobate . Internal structure can be preserved: it is formed by successive pads of sedi­ment which can be expresed on the exterior as ribs. The ribs are arranged in a chevron -like biserial pattern along the external or internal dorsal part. Exterior smooth mantle coverin g the structure and /or oval m ound -like terminations of the trace fossil can be present.

Diagnosis. Horizontal to subhorizontal keel-like bilobated trails, composed of chevronate ribs arranged to form a carinate pattern. Trail cross-section trapezoidal, amygdaloidal to triangular, preserved as both convex/concave epirelief and positive hyporelief (emended from Han & Pickerill 1994 and Uchman 1998).

Remarks. The morphological features of Protovirgularia are similar to several other horizontal trails, such as Cruziana, Scolicia,Nereites, and Psammichnites. The bilobate Cruziana has numerous scratch markings on both sides of the furrow, a feature never observed in Protovirgularia. Bilaterally symmetrical Scolicia lacks chevronate ribs that are typically developed in Protovirgularia. Nereites has a wider median furrow rather than a central string, and the closely spaced lobes on either side of the furrow never chevronate when compared with Protovirgularia. The lack of a median dorsal structure (e.g., straight ridge/groove) distinguishes Protovirgularia from Psammichnites.