Spirodesmos milanai Aceñolaza, 2005

Diagnosis: Spirodesmos displaying from 1.5 up to 6 irregular close whorls, developed non-concentrically to each other, frequently following and overrunning earlier loops.

Description: One-way irregular spiral burrows, with 1.5 to a maximun of 6 turns and no central turnaround. Circular to elliptical in section, mostly preserved as convex epireliefs, frequently slightly compressed vertically. Traces may display linings (0.4–0.8 mm thick). Burrow diameters are quite regular, ranging from 40 to 60 mm. Filling massive. Individual loops are developed close to each other, slightly eccentrically but following and overrunning an earlier loop. Diameter of whorls varies between 120 to 800 mm, with a reduction of the same 2–10% recorded in every turn. Most commonly, traces are found associated in different diameter sets, frequently overrunning and intersecting each other.