Circolites kotoucensis Mikulaš, 1992

Description.  Circular pits, relatively shallow (the pit diameter:pit depth ratio is 2:1 to 4:1 in specimens interpreted as non-truncated). The angle between the pit wall and substrate surface is 50°–110°. Pit diameter is 10–75 mm; measured depth is 4–24 mm. Substrate angles towards horizontal direction were measured on rock surfaces not detached from the bedrock. These vary from 0° to 120°; in other words, they vary from horizontal to moderately overhanging. The pits usually do not touch each other, with two noteworthy exceptions and a couple of analogous but poorly preserved samples. One cluster (Figure 5(C,D)) shows a ground plan resembling a flower of a rosacean plant with five petals. Two of the ‘petals’ represent complete specimens of Circolites, while the remaining three ‘petals’ are partly consumed by their neighbours. The surface is significantly smooth. The size of the whole structure: diameter 78mm, depths of the ‘petals’ 87, 48, 38, 38 and 41 mm. The large five-petal structure is intersected by four much smaller borings (Gastrochaenolites isp.). The second mentioned group consists of cup-like depressions joined into a linear chain with a smooth bottom, found on a horizontal surface (Figure 5(E,F)). Undoubtedly, eight pits can be recognized. Their centres are situated in a nearly straight line. Pit diameters are not exactly constant; they are 55–103.5 mm. Surfaces of the pits are conspicuously smooth. Their shapes resemble spherical caps showing the depth:diameter ratio of about 1:4.

Diagnosis: Shallow, roughly circular pits in carbonate substrates. The peripheral edge of the pit is sharp, the walls of the pit are perpenticular to or overhanging the substrate surface. The edges of some pits are undulated, the pit bottom is moderately concave. The diameter of pits is usually 10 to 4mm, their depth 3 to 10 mm. They were formed by boring echinoids. The pits often occur in major groups, in some cases touching one another.