DHE 16 with high solid rib-any info available?

[nid-28]

I recently acquired a DHE 16 ga. on the one frame with a Miller SST. The number is 231081. No records appear to be available. I'd like to learn what I can about the raised solid rib that is on this gun. I've not seen one before except on a Pigeon gun. Can anyone shed some light on this type rib? In addition, this gun has a sharper curved (radius) pistol grip, which is different from every other Parker I've owned over the years. It feels totally different when you bring the gun to your shoulder! Your wrist is almost straight up and down. Thanks for all your help and Happy Holidays!! PS--I'm not sure why my photos load in upside down. They are right side up on my computer when I look at them!