This matched pair are fossil trilobites from House Range-Antelope Springs in Millard County Utah in the U.S.A.

SIZE:(in millimeters) 25 x 18 x 2.5 to 3 MM THICK EACH STONE.
WEIGHT(Carats): 28 TOTAL WEIGHT OF BOTH STONES. 
DOME: NATURAL FOSSIL.
BOTTOM: NATURAL NOT CUT.  
EDGE:  NATURAL NOT CUT. 
POLISH:  NATURAL NOT CUT