Unknown flat housing port

I got this flat glass port, maybe for an underwater housing, with a bunch of second-hand Subal housing stuff on Ebay from a reseller.
The port is 90 mm outer diameter, has no markings of any sort. It has three O-rings, two by the bayonet mount, and one on the outer ring surface.  

Your kind help in identifying it will be greatly appreciated.

That certainly is a Subal bayonet, but don't know if it is T3 or T4

Bill

  I have both the T3 and T4 Subal ports, and this unknown port is smaller than the T3, the bayonet lugs are also smaller and with rounded corners, so it is not Subal.

 Good try, but port identity remains unknown.