Kingdom: Amoebozoa
Phylum: Mycetozoa
Class: Myxogastria
Order: Liceales
Family: Reticulariaceae
Genus: Enteridium
Species: E. lycoperdon
Binomial name: Enteridium lycoperdon (Bull.) M.L. Farr, 1976.
Synonyms: Reticularia lycoperdon (Bull.), Fuligo lycoperdon (Bull.) Schumach, Lycogala punctata Pers, Lycogala turbinata Pers, Mucor lycogalus Bolton, Reticularia umbrina Fr., Strongylium fuliginoides (Pers.) Ditmar.

Enteridium lycoperdonis a cosmopolitan slime mould whose habitat is decaying wood. It can be quite variable in size and colour. Usually, it has a cap diameter of 5-80mm. It appears frequently throughout the year but is more prevalent during Spring. The plasmodium stage is white and is more or less rounded. A mature fruiting body takes on a silvery white colour from spore deposits. The dry, spongy interior produces copious amounts of red-brown spores in the manner of a puffball which it is not.

A new fruiting body.
[1]

A mature fruiting body

[2]

Photo of the underside of the fruiting body when removed from the wooden host.
[3]

Here the fruiting body is cut open to show the tightly packed spores.
[4] 

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/