For sale here is a Brown Bivisible tied by the late Edward R. Hewitt.
An excerpt from page 278 of Trout Fishing in the Catskills by Ed Van Put follows....."Perhaps the best known fly that he created, and his personal favorite, was the Brown Bivisible."
This fly comes from the collection of a Sullivan County sportsman who, as a kid, grew up around many of the legendary Catskill fly tiers. His uncle was also close friends with many of them. His Hewitt flies were acquired from the Holmes family, who were caretakers of Hewitt's estate on the Neversink. Further provenance details will be provided upon request.
I have two of these flies for sale in separate listings.
Disclosure on all of the "original" Catskill flies here on my website: I did not see these people tie these flies, so I cannot tell you they are 100% authentic. I do however consider my client and his provenance to be absolutely credible. Also, Dave Catizone has inspected each fly in his collection, written up authentication letters for the framed flies (some for sale here), and told me he believes the unframed, individual flies to be authentic as well.