Dogs and mushrooms?

[WELOVESPUPPIES]

I just found this dried up black thing on Chopper's blanket in our office, something he must have brought in last night. I think it is a dried up mushroom. I saw him trying to eat it this morning before I realized what it was and picked it up. Should I be concerned? Should I induce vomiting? I know that mushrooms can be toxic but I am not sure that is what it is or how much he ate. I cannot think of anything else that he may have gotten off the patio (we have pavers and the occasional mushroom grows through).

EDIT: It was, I just checked the patio and where there had been a dried mushroom the other day it is gone now, just the stain where it was. What should I do my vet is not open yet to ask them?? Now I am concerned that he actually ate most of it last night hiding in the office. Would I notice by now if it was going to cause a problem? He seems fine this morning.

EDIT: Well I managed to reach the emergency vet in our area...she made it sound like I needed to get him to the vet right away with a sample of the mushroom because it could be very toxic for him (by the way she was rude...it wasn't like I was feeding him mushrooms but that is how she talked to me!!) My vet has opened now and I called them. They told me just to monitor him for any unusual behavior...I am confused how can one person be so worried and another be like...well lets watch and see. He seems fine but how long would it take before I noticed something wasn't right and by then would it be to late?? Should I make him vomit incase he swallow some this morning? Vomiting is something they told me to watch for...so far nothing. I looked on line and found a mushroom that looked like what I had seen grow in that spot earlier this summer, it was toxic.