We have systematically investigated the magnetic, electrical, and structura
l properties of the high-purity superconducting ferromagnet RuSr2GdCu2Os8 i
n which superconductivity and significant ferromagnetism have been reported
to coexist. Our results show that there may exist in this compound a novel
superconducting state which is characterized by the absence of a bulk Meis
sner effect, the presence of negligible superconducting condensation energy
, and the appearance of an unusually large effective penetration depth. Suc
h a state appears to have a nonuniform filamentary structure existing in th
e less magnetic walls between the ferromagnetic domains or a fine-grain str
ucture beset by ferromagnetic walls between antiferromagnetic "domains," si
milar to the case of NdNi2B2C. These results are presented and contrasted w
ith the recently reported Meissner effect in RuSr2GdCu2O8 in terms of the v
arious phase transition sequences predicted.