Last year I was in Milford haven for a few days and went to some places where I know mushrooms are regular. There was one particular mushroom that puzzled me at the time. It had a dark brown, almost black cap and prominant umbo. It was large and fleshy and had veil remnants. The stalk was clearly tapered and darkening towards the base. Its cap was shiny when wet but matt when dry. I thought, given its strong features that it would be easy to identify. It wasn't and I didn't know what it was, until today.
Through sheer luck whilst searching for something else I came across it in a book, then searched online to help my verify it.
It turned out to be Agrocybe erebia/Dark Fieldcap.
The cap is dark and wavy, with a prominant umbo. The stem is thick, fibrous and tapers at the base where the colour gets darker towars the end. It's gills are an umber-brown colour.
It also has a ring that sometimes can be found. When young the veil resembles an opaque white membrane which collapses with the most gentle of touches. Click on the photo below to view the veil better.
below is a phot of more mature examples. As can be seen the umbo is clearly prominant but the colour of the cap is much more brown.