Vlasto 1659 (this coin), the plate photo is quite poor, though the obverse is precisely the same the reverse is weak probably due to the fact that it was a poor cast and it appears that most if not all the photos in Vlasto are based on casts not the actual coins. The positioning of the kantharos on the reverse is the same as on the actual coin. Ravel does not note the dot in the field or the aplustre for the simple fact that they did not transfer when cast for some reason. This is the most likely explanation.
O: kantharos, letters in right field
R: kantharos, dot in right field, aplustre in left field
Ex: Michel P. Vlasto (1874-1936) Collection
Ex: Den of Antiquity (UK)
Photo of M. P. Vlasto from the frontispiece of Descriptive Catalogue of The Collection of Tarentine Coins formed by M. P. Vlasto, compiled by Oscar E. Ravel (reprint 1977)
Click on the link below to see an example of a nice Southern Italian Kantharos like those depicted on this obol: http://www.hixenbaugh.net/gallery/detail.cfm?itemnum=3252