Hi Andres,
The top pic appears to be what Deepeeka market as a 'Burgh Castle' type ridge helmet, and the bottom pic seems to be a different interpretation of the same style, without the Berkasovo 'collar' between the bowl and guards. As far as I can recall, this is the only Late Roman helmet found in Britain. Roman Army Talk often discuss Late Roman Helmets - if you have an interest in the period, do go & have a search, or indeed join.
http://www.romanarmy.nl or see my group's website
http://www.comitatus.net/ We have a couple of helmets in the group in this style.
The main problem is that only the top of the bowl was found at Burgh, so most reconstructions assume the cheek pieces and neck guards are similar to so called 'cavalry' helms of Bekasovo and/or Duerne because it doesn't seem to have ear cut-outs like the Intercisa ridge helmets. Stephenson appears to be happy that it had a nasal, but I only see some possible fragments.
The best pic I have seen is in Stephenson, I.P. 2006 Romano-Byzantine Infantry Equipment, Stroud: Tempus p24 I understand the usual reference work is: Johnson S, A Late Roman Helmet from Burgh Castle, Britannia XI, (1980) pp303-12
According to Bishop & Coulston, the Burgh Castle example was similar to the Concesti helmet (although that did appear to have rectangular ear cut-outs) and another found "recently at Independenta" - perhaps Heteny? It has an undecorated iron four piece bowl. Each half consisted of two non-touching plates rivetted together by a wide tapering band. Burgh Castle is in Norfolk & was only built in the C4th.
The middle pic might be a speculative reconstruction of a hybrid between a spangenhelm and a ridge helmet, but I don't know of any find it resembles and don't personally like the look of it.
Feel free to get back to me, e.g. on the helmets I or other Comitatus members choose to wear.
Hope that's helpful.