Thanks, Jason, for the data and for your opinion. I think that, according to your suggestion, A. conoidea is the best choice for this specimen.

A. conoidea – spores 12-19 × 6-9 µm
A. macrospora – spores 19-26(-28) × 9.5-12 µm
A. salweyi – spores 20-35 × 10-15 µm

Also A. conoidea and A. macrospora share a character of the involucrellum – it spreads away from the exciple so that it is not continuous below the perithecia.

A. conoidea – perithecia with ostiole often projecting as a papilla; thallus usually immersed; abundant on hard limestone and calcareous walls in shaded, moist situations
A. macroscpora – perithecia without a distinctly papilla-like ostiole; thallus superficial; on sheltered siliceous or weakly calcareous rocks in coastal areas (also describes perithecia as “flattened”)

Among these choices, A. conoidea is definitely the way to go. Your spores are on the large side, but within range of known variation. Stated variation can mean either that the average for all specimens should be right in the middle of the given range, or it can mean the average measurements for any one specimen should fall somewhere within the given range for 95% of specimens. If the latter interpretation is correct in this case, then your measurements are fine for A. conoidea.

One last note: yours has abundant pycnidia; British Flora claims A. conoidea has “frequent, often numerous” pycnidia (conidia 3.3 × 1.5 µm), while A. macrospora has “usually few” pycnidia (doesn’t give measurements of conidia).

of this specimen revealed 1-septate spores, with true eusepta, having the following dimensions:
Me = 17.6 × 8.4 µm,
which immediately rules out Verrucaria as well its segregate genus Bagliatoa, and points to the genus Acrocordia instead. There are no so many species in this genus. The more common, having calcareous rocks as habitat as this one, is A. conoidea, but has smaller spores. All the others I know can be ruled out as follows:
- A. gemmata lives on bark;
- A. salweyi though living on rock has spores with Spores dimensions 20-35 × 10-15 µm.(see lichens.ie);
There is another one, A. macrospora, which also lives on calcareous or silica-poor costal rocks, for which I could not find information about the dimensions of the spores (see lichens.ie).
I upoad already some bad photos of the microscopy, which maybe are the last that will present from this microscope, that has a broken piece that will not permit to take further photos.