Large numbers of eggs ofFundulus heteroclitus have been found in shells of the intertidal mussel,Modiolus demissus, near Wachapreague, Virginia, during six consecutive summers and in Brown’s Bay, Vírgínia, during 1972. Egg deposition in shells in aquaria has been observed. This behavior may serve to protect the eggs from predation. In nature the eggs in shells are exposed to high temperatures and desiccation for long periods during lower tide levels. Hatching has occurred in 14 to 17 day under these conditions. Eggs taken from mussel shells and eggs stripped and fertilized in the laboratory did not have chorionic filaments or the filaments were greatly reduced in number and length. The habit of egg deposition in shells and the morphology of the eggs are different from that reported forF. heteroclitus from Woods Hole, Massachusetts.