Perhaps one comment towards the location of the harbour. An archaeologist told me that the location of the harbour shown on the reverse of the coin is not at the Tiber river mouth but a bit north from Ostia close to the "Lago di Traiano" and the "Leonardo da Vinci" airport. Therefore, may be, the figure at the bottom is not the river god Tiber but most probably Neptune.
The deity at the bottom bears all attributes of Neptune indeed; it cannot be the
Tiber river-god; river-gods are usually represented reclining on
rocks, holding a
reed (see
http://www.acsearch.info/record.html?id=38521)
As to the upper statue, it is hardly recognizable, but it is not Neptune, which would hold a trident, not a
scepter. Maybe the deity is radiated, as seen on
http://www.acsearch.info/record.html?id=14779 below.
By the way, some
auction descriptions describe correctly this
reverse, like in the coin above.
Nice coin BTW, very natural surfaces.
Jérôme