An ouroboros surrounding a skull necklace ... skull and ouroboros jewelry.
The scaly endless serpent snake devouring its tail is called the ouroboros and is symbolic of continuous renewal, the cycle of birth and death, and infinity.  
The skull is symbolic of mortality and a reminder that death comes to all living things ... the Latin sentiment MEMENTO MORI means remember your death and is meant to inspire you to intentionally think about your own death every day, as a means of appreciating the present and focus on the future.

- approximate measurement - ouroboros just shy of 5/8” (15mm), skull almost 3/8” (10mm x 8mm)
- charm metals  - sterling silver (.925 silver)
- photographed with a US dime for scale
- charm only - the chain is sold separately here 

This endless ouroboros snake serpent watch key charm has been reproduced, and altered a bit, from an antique Georgian era (1714 - 1830) watch winder key from my private collection of interesting novelty watch keys.
See the original ouroboros watch key in the photo.  It's available here.
And just the plain ouroboros charm is here.

The skull is hand crafted from just a portion of an antique Georgian wheel wax seal (1714 - 1830), shown in the photographs, the full size wax seal depicting a skull surrounded by the Latin sentiment ES FVI SVM ERIS which translates YOU ARE, I WAS, YOU WILL BE.
See the wheel wax seal from which the skull was created in the photo. 

The ouroboros surrounding a skull necklace is also available in mixed metal, a sterling silver ouroboros surrounding a bronze tiny skull, shown in the last photo and available here.
Find just the tiny skull charm here.

Impressed with history!
©2019 suegray jewelry