Sciency Thoughts has a story about pyritized trilobite eggs.  The eggs were found associated with 2 Triarthrus eatoni trilobites from the Ordovician Whetstone Gulf Formation (Lorraine Group), in upstate New York.  The eggs were found in the cephala (head) of the trilobites, which is similar to the method of reproduction in Horseshoe Crabs.  In Horseshoe Crabs, the males cluster around the females as they secrete eggs in order to fertilise them externally. 

The original paper appeared in the January edition of the Journal Geology.  It is entitled “Pyritized in situ trilobite eggs from the Ordovician of New York (Lorraine Group): Implications for trilobite reproductive biology” and was authored by Thomas Hegna of the Department of Geology at Western Illinois University, Markus Martin of Watertown in New York, and Simon Darroch of the Department of Earth and Environmental Sciences at Vanderbilt University.