Following on from my previous post, there is a lively discussion going on at Ancients.info on the early unmarked coins of London and, in particular, the intermediate group first proposed by Bastien. Since RIC VI was published in 1967, there has been a significant amount of research on these series and a number of significant articles have been published. The following are amongst the most important:
Bastien, P. & Vaselle, F. - Le trésor monétaire de Domqueur (Somme) Wetteren, 1965.
Bastien, P. - Some comments on the Coinage of the London Mint, AD 297-313 NC 1971, p.152-156.
Amandry, M.- Un follies inédit de Dioclétien pour l’atelier de Londres BSFN, April 1980, p.677-679.
Bastien, P. -Atelier Continental sans Marque Le Monnayage de l’Atelier de Lyons, Wetteren 1980, p.125-128 (pl.LXIX).
Burnett,A.M. & Robinson,P.H. - The Upavon, Wilts, hoard. CHRB, Vol.V, BM 1984, pp.90.
Stewartby - Early Tetrarchic Coins of London from the Market Stainton Finds NC 1998, p.89-102 (pl.28,22).
Besly, E. - A Hoard of Tetrarchic nummi from Bridgend, South Wales NC 2002, p.169-215 (pl.31-42).
Drost, V. & Gautier, G. - Le Trésor de Larré (Morbihan) : une thésaurisation mixte de la 1re Tétrarchie (terminus 300 après J.-C.) Trésors Monétaires XXIII, 2009, p.1-33 (pl. 1-10).
Essentially. the current thinking is that as well as the “unmarked continental mint” with its plain laureate busts, there is a further group of plain laureate busts attributable to London with its distinctive small, neat lettering – as opposed to the big, irregular letters with slender down-strokes of the Lyons style. Stewartby gives these London plain busts the designation Class Ib with the LON issues being assigned to Ia. There then follows a new series designated as IIe that comes before the IIa class described in RIC VI as "with small head on tall neck".
Class IIe are all cuirassed but have busts that are reminiscent of the Lyons style. Stewartby is careful to point out, however, that there is no definitive break between IIe and IIa and goes so far as to describe a series IIea into which ambiguous coins can be placed.
Stewartby describes the Ib and IIe series combined as the “intermediate group” although it is not clear to me that this was Bastien’s original intention. In his 1971 NC article he seems to describe the IIe series alone as the “intermediate group”.