I hope someone can help me with this one. It reminds me on Lophiostoma, but I did not find a fit there. I also stumbled over Kirschsteiniothelia which looks similar, but I have not enough Literature.

Substrate:  Wood, probably coniferous, but I'm not sure. The fruitbodies are partly overgrown by a corticioid basidiomycete (Hyphodontia aspera).

Macroscopic description:

Fruitbodies immersed, semiimmersed or nearly superficial, about 0.4-0.5 mm in diameter, black, with a slit-like opening.

Microscopic description:

Perithecial wall with very dark brown, mostly isodiametric to somewhat elongated cells, thick (partly >100 µm).  Asci bitunicate, J-, 90-120x10-12 µm. Spores dark brown, two-celled, constricted in the middle and often rather pointed outwards, with several small drops in water and mostly two large drops in CR or J, 15-18 x 6-7 µm. Spores have an inconspicuous  but rather large slime sheath.

Thank you for any help

Stefan