Roman coin help [επιλυμένο]

Hello all,
I have this coin: https://en.numista.com/catalogue/pieces133030.html
except size is 18.2mm with an oval shape and the letter in the field is D
it is Arles mint ( PCON )

My questions are:
What is the letters in the field?
Would it still be listed as this coin in the catalog ?(assuming its the same denomination)

It should be this one: http://www.wildwinds.com/coins/ric/constantius_II/_arles_RIC_viii_215_2.jpg
Size and shape differences are common on antique coins. The D is possibly just a little detail that was added after a new die was made. Letters in the fields of the coin are also mentioned in this article about identifying roman coins: https://www.all-your-coins.com/en/blog/antique/romaines/comment-identifier-les-monnaies-romaines

Ok, thanks for the help. I'll get it added to the catalog as soon as I can get some clear pictures.