Ancient Roman, Byzantine, and Anglo-Saxon Gold Signet Rings

Total of 4 Ancient rings:

Bull Roman Signet Ring (5.5 g)

Dolphin Signet Ring (3.1 g, 18.9mm internal diameter, 2nd-3rd century AD)

Cross Ring (I'm fairly sure this is different time period than the others, maybe byzantine, 6.8g, 6th century AD, 18mm inner diameter) 

Last is not a signet ring, with just a spherical garnet stone and an early anglo style gold band (4.1 g, 20.2 mm internal diameter).