The Square one is an alternative to the No.6 or Flag or Igniter (IEC = R40). There are versions with two screw terminals. It's a lot smaller than a #6 cell.
The #6 can come in version with one terminal and wire or two terminals too.
I'd love a 300dpi scan of it. I only have poor photos.
It's an Ever Ready R1662
Here are a couple that didn't sell on 7th Aprilhttp://www.ebay.co.uk/itm/190819071857
I have a picture of various Siemens cells, 3 square cross section 1.5V, F size, this size and No.6 Size, from an ebay listing. I'm sure I've seen US versions, but my US Eveready shortform from 1955 only has the F, G (964) and No.6 (Ignitor) based single cells.
A DEAC is similar design case, but smaller even than an F cell.
I just noticed the US Eveready 740 is a staggering 18 x F cells in parallel (that's 9 of the 800 packs in size, the 800 pictured is 2 x F cells) 6lb weight = 2.72 kg! . The 776 is even bigger having 18 x F cells for 9V tapped at 7.5V and also 90V via layer cells. 14lb 12 oz. The 758 must have smaller layer cells as it's 14lb 4 oz (also 18 x F cells)