In the Boston area, most mid-18thc stones share basic design elements. There will be a death's head or sould effigy on the tympanum, accompanied by floral or other organic-y borders and a roundish finial design.
Things are different in Rhode Island.
There's a much wider variation, especially in tympanum designs. While most soul effigies and death's heads in Boston are variations of a carver's signature design, lots of stones in Rhode Island have images that are either unique to indivdual stones or very rare.
One such stone is the Thomas Westcot stone (1745) in Providence:
The Kathrin Hawkings stone (1749) has a similar, but not identical design.