There are 5 species of mammals that lay eggs and they are called 'monotreme' https://en.wikipedia.org/wiki/Monotreme
* Platypus (Ornithorhynchus anatinus).
* Short-beaked echidna (Tachyglossus aculeatus).
* Western long-beaked echidna (Zaglossus bruijni).
* Eastern long-beaked echidna (Zaglossus bartoni).
* Attenborough's long-beaked echidna (Zaglossus attenboroughi).