According to my copy of 'The Severance Genealogy' by David C. Dewsnap, who's work I've read in different posts is accurate for the most part, says Charles Leland is the 6th great grandson of John and Abigial Kimball Severance.
His line is as follows :
Charles Leland m: Laura Mae Plante
Bertrand Ernest Severance m: Lillie E. Bombard
George Severance m:  Betsy Cook  Eveline Sanger
Ebenezer Severance m: Jerusha Kilbourn [Kilby]
Ebenezer Severance m: Lucy Nutting
Ephriam Severance m: Abigail Trask
Ebenezer Severance m: Anna Fitts
Ephriam Severance m: Lydia Morrell
John Severance m: Abigail Kimball
All of these Severance's were born in the U.S. John & Abigail came from England.
I have more information on Lydia Morrell's parents, as they are my husbands ancestors also. Let me know if you'd like it.
The Severance Genealogy is available thru Heritage Books. 1 800 398 7709 at least that's where I bought my copies.
There are several Nicholas' in the book, but no Nicholas Arthur. I can look him up if you have his birthdate or some other info I can match up.
I haven't seen any mention of a family crest.