Syme, "The Ummidii", Historia: Zeitschrift für Alte Geschichte, 17 (1968), pp. 98f
roman-emperors.org
DIR contributor (Herbert W. Benario, 2000), "Hadrian".
uchicago.edu
penelope.uchicago.edu
The epitomator of Cassius Dio (72.22) gives the story that Faustina the Elder promised to marry Avidius Cassius. This is also echoed in HA"Marcus Aurelius" 24.