Within about a half hour period around noon today, I saw 5 of these slugs crawling on a dry sidewalk. One slug had already run out of steam, or rather, liquid water, in the middle of the sidewalk and was rapidly approaching its demise. I relocated it to the grass along with the other 4 who were totally oblivious to the risks of crawling on bone dry concrete.
They were about 2 to 2.5 cm long and black. Very Black. I had to lighten up the pictures in Photoshop considerably to make their skin features visible. I believe they were Deroceras laeve.