Illaenus wahlenbergii (EICHWALD 1825) . This trilobite was found in the Vilpovitsy quarry, St. Petersburg region, Russia

Dates to the Middle Ordovician Period.

Size: Trilobite - 5.5 cm x 3.0 cm (in straight projection)
Matrix: 6 cm x 5.5 cm x 2.5 cm
 
The hard calcite exoskeleton shows up nicely against the lighter limestone matrix.