I've been trying to hook one of these for a long time but could never afford one but today,I bit the bullet when I came across this one in a store I don't often buy from.He buys all of his ancients from Gordon Andreas Singer,a local expert who has written many books and papers for all of the major coin publications. This issue is actually quite well known,featuring the two male heads in the comedy/tragedy pose and the reverse of a sea eagle sitting on top of a dolphin holding on with his claws and attacking with the beak. I found this on Wildwinds:"Although numismatists have put forth many theories to explain the curious obverse type of the Istrian coins with the two heads tête-bêche, the most plausible explanation is that the design represents the two branches of the Danube River." I can't believe I finally got one.
Thanks Bone, You'll get a kick out of this.Julia Mamaea,daughter of Severus Alexander,borrowed the eagle/dolphin design for the reverse of one of her coins,over 600 years later.Apparently she was born near Istros.