On a fallen Fagus branch we found these bumps, sometimes black broken through, under which black perithecia are visible, without a black ring around the stroma.
The perithecia have a neck (not clearly visible in the photos) that is about as long as the bulb and lie just under the bark in the horizontal plane, usually with 3-5 together .
The spores are brown with 3 septs and show large guttulles, usually one in each segment.



We found Prosthecium ellipsosporum, which could fit some spore size and also does not have a black rim around the stroma, only this one has been described on Carpinus and these spores have appendages.
Maybe there are other options?
Thanks in advance, Margot&Geert