NOT IN RIC
UNLISTED BUST TYPE - E1. RIC lists for this reverse only two bust types: B1, head r., laur. [CONSTANTINOPLE 16, off. Γ] and E2, head r. with rosette-diadem [CONSTANTINOPLE 22, off. Γ and CONSTANTINOPLE 22, off. S] (p. 572-573).
However, classification of diadems on Constantinople coins is not very precise. The bust type of CONSTANTINOPLE 23 is also classified as E2, although in footnote 23 on p. 573 Bruun mentions specimen "with threefold pearl diadem". The same problem occurs with Constantiniana Dafne issue [CONSTANTINOPLE 29-35]. In footnote 29 on p. 574 Bruun writes as follows: "The distinction between the plain diadem and the rosette diadem is at times rather arbitrary. Diadems, structurally consisting of bands adorned with pearls and jewels and with small forehead jewel, if any, have been classified as plain diadems". Compare the presented specimen with three other specimens from the same issue. The first with undoubtedly rosette-diadem [click for picture], the second, also rosette-diadem, but with large pellets and square rosettes [click for picture], and the third, from Victor Clark's collection, with diadem which still resembles a plain ladder-shaped diadem [click for picture].
Coin should be listed before CONSTANTINOPLE 22.
CONSTANTINOPLE [before 22], CONSTANTINE I, UNLISTED BUST TYPE [E1], OFFICINA S