Carsten, the traditional Dallmeyer Patent Portrait "A" type lenses are petzvals, not rectilinears. By checking the serial number here, you can be sure. Similarly with a lot of Dallmeyer designs, the numeral in the designation indicates the size. Therefore a 3A and 4A are the same design, F4 petzvals, with the 4A being larger.

You can get a good description and picture on about page 15 of an old catalog here: