Constantius II. AE3. Trier. 

D N CONSTANTIVS PF AVG, pearl diademed, draped and cuirassed 
bust right with long thin neck
(FEL dot TEMP dot R)EPARATIO, radiate phoenix standing right on 
rocky mound. 

Mintmark TRP dot or TRS dot. 

RIC VIII Trier 227.

These long thin necks on Phoenix coins can only be seen
from the Trier mint.

With permission of Roma Numismatics, October, 2009