Round object below snake in basket: Strack p. 164 thinks it is a situla, Isis' normal two-part water container, hanging from her left wrist in the coin type: "am Handgelenk hängt das der Isis eigene zweiteilige Wassergefäss".
Thanks so much for the explanation, @curtislclay. Strack appears to be the only authority to have even tried to account for this mysterious object. It certainly makes sense that Alexandria would have some more of the attributes of Isis in Romano-Egyptian iconography -- just like "Aegyptos" -- given that she already holds a sistrum. Wikipedia describes a situla as a bucket or pail, and specifically mentions it as an attribute of Isis. See https://en.wikipedia.org/wiki/Situla: "The term is also used for pails carried by figures in other art forms; according to Plutarch and other sources this was a sign of a devotee of Isis, who herself is often shown carrying one (containing water from the sacred Nile), of a rather different shape, with a rounded bottom, and sometimes lidded. This rounded shape, often with a "nipple" at the bottom (see Luristan example in gallery), is believed to have represented the female breast.[14] These were also donated to temples as votive offerings by devotees." Here's an image from Wikipedia of a priestess of Isis carrying a situla: And the referenced situla from Luristan from the Wikipedia gallery: Here are some examples of the Hadrian Travel Series standing Alexandria type from acsearch on which the object is depicted as something other than an untethered round ball hanging in mid-air: Savoca 2020: Emporium Hamburg 2019: CNG 2018: Do these fit the description of a "situla" carried by Isis? They all do seem to have the nipple shape at the bottom, so that matches. My verdict is that the explanation makes a great deal more sense than any other I've heard, which is none!
Donna, Your additional illustrations make me too think that Strack is probably correct to see a situla below the snake in basket.
The auction description of my Hadrian Travel Series denarius depicting Alexandria stated as its provenance that it was purchased from Seaby in 1990. The coin arrived today, and the package included the old Seaby coin envelope as documentation: Judging from the third image, the 1990 purchase date looks like the consignor's best guess. Perhaps "no later than 1991" would be more accurate. Dix Noonan Webb, of course, did not disclose the identity of this collector. I'd certainly be curious to know who it is or was. I only visited Seaby once, when I was in London in 1986, but remember it very fondly. I spent at least a couple of hours sitting at the counter looking at tray after tray of British gold coins and silver crowns, a number of which I bought. They were very friendly. By contrast, Spink seemed very intimidating to me -- it looked more like a bank than a store, with the entire premises hidden behind locked doors and a bulletproof window with a slot in it to pass items through. I left after about 60 seconds! Browsing certainly didn't appear to be encouraged.