The two look similar, but if you look at the B2215, its lens has diagonal prisms in the top left area of the visable portion while the clamshell doesn't appear to have that. It could be a modifyed design though of course as the rear portion and bottom prisms look identical... Westie switched refractors on the OV-15 in the 60s from a more curved design to the more angular design that's still used today.