The use of American opossum as a fly tying material is a recent thing as far as I can tell. Some tyers have found it useful as a seal fur substitute. Some thought on the word opossum here:

https://www.grammarly.com/blog/opossum-vs-possum/

That fly is in “Brook and River Trouting” by Edmonds and Lee. They obviously got the spelling wrong because American opossum is never mentioned in British fly tying literature but Australian possum frequently is. https://books.google.com/books?id=mv01DwAAQBAJ&pg=PA255&dq=pale+watery+dun+opos...

See the edge of the natural brown possum.

https://wearnewzealand.com/possum-nz

I have a lot of Corticelli Belding silk thread. Here is a chart showing relative sizes of silk thread.

http://www.bestfromjapan.com/moreinfo.c ... t_id=13490

Gossamer is considered to be slightly finer than 6/0.

I’m surprised that the author was able to find enough information about Marryat to write a book. The pictured fly encapsulates the founders of the dry fly movement: Halford, Marryat and Hall.

http://flyanglersonline.com/features/journal/part61.php

I don't know of any flymphs but there are lots of emerger patterns.

I think the kit fur has fewer guard hairs. The picture shows a kit muskrat skin. The color is unusual though.

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