I don't pretend to know very much about C.I. cookware...but the deep, interlocking rim, the apparent extra depth of the long-spike bottom, along with the way the hinge seems to be anti-separable when closed...all suggest a copious, thick, heavy batter that expands considerably with heat. Think Yorkshire Pudding-like, or Dutch Baby (which are both thinner batters, but...). Those spikes, as D_Madden suggests, would add much in the way of quicker, more even cooking. The thing would have to be very well-seasoned...all that surface would sure grab hold of the product, otherwise.
Also worth considering is the mark PAT APLD FOR, in raised letters, and set in a curve...not common in contemporary manufacturing. Note that the outline of the bases of many of the spikes can be seen on the marked upper surface, which seems to indicate an unusual type of Pattern. The nubbly finish is admittedly similar to modern production but appears more so on the inner flat surface than, say, on the outside of the cover.
I think it's got some age...too bad it isn't otherwise marked. A nice piece, DavidF!