Take a look at these photos of Pisolithus tinctorius and/or arrhizus (which may or may not be the same mushroom):

http://www.mushroomexpert.com/pisolithus_tinctorius.html
(And check the links at the bottom of the page.)

http://www.mykoweb.com/CAF/species/Pisolithus_arhizus.html
(And more links at the bottom of this page.)

http://garden-photos-com.photoshelter.com/image/I00009dGRQ9EDXfU

Thanks for the links. Looks like that could be what it is. Ugly little sucker.

Because of its mycorrhizae aspect, I wonder whether chopping it up and placing it in the compost pile would be beneficial to the finished compost?

I'm afraid I have no idea what it would do to your compost. The folks on GW's Soil forum could probably tell you.

Chopping up the mushroom won't benefit the compost, at least not until the fruiting body produces spores. Then, the spores have a chance of growing into a mushroom population wherever the compost is used.

It is only the underground mycelium and hyphae from living fungi that are capable of developing a mycorrhizal relationship with the roots of certain plants. The aboveground fruiting body (mushroom) is simply the spore producer.....a sign that the important part of the fungal organism is thriving within the shallow depths of the soil.

Make sense?

It does make sense, rhino_1. Thanks for the explanation.

I appreciate the responses here. Cheers!