This is a John Holland Jewel Inlaid Pearl and Black Stripe ringtop pen c. 1937-1938. The pen barrel and cap appear to each be made from three separate pieces that are probably glued together. The two end sections of the cap and barrel are a rounded solid black plastic. The center is a tube of alternating wide black and narrow faux mother of pearl strips and given the name, the pearl elements may be inlaid. It was offered as a full size clip pen, a ringtop, as shown, and as a ringtop with a clip. It has a Number 2 size 14 karat gold nib marked "JOHN" over "HOLLAND" over "CIN. O." and is 4 1/2 inches long capped, 5 1/2 inches long with the cap posted on the end of the barrel. Retail price was $6.40, and the matching pencil was $4.50.
I've been able to find a bit more information about the John Holland Jewel Inlaid Pearl and Black Stripe pens and updated the article on PenHero.com. You can read more here:
John Holland Jewel Inlaid Pearl and Black Stripe c. 1937-1939