PLEASE HELP IDENTIFY- Strange Egg Like Rock / Fossel & Shell Like Features

Found this egg like rock digging when I was young. Decided to see if anyone can shed any light as to whether its characteristics are that of a prettified egg or some other potential geological reason for this strange formation. Regretfully I pulled of much of the shell like casing when I first dug it up. The shell like casing has a very thin inner layer and a much thicker layer.