This looks more like a sheep than a lamb, right? It is among the first degree symbols in Cross’ Masonic Monitor.
Also in Webb’s Monitor we have a sheep which is printed with the text about the apron being of lamb skin. Perhaps it is a lamb after all.
Top: The True Masonic Chart of Hieroglyphic Monitor (1826) by Jeremy Cross (available on Archive.org)
Bottom: Webb’s Monitor, Morris’s Edition, 1872