Melusina was a mythical figure from European folklore, a water nymph who is often portrayed with the upper body of a beautiful woman but the lower that of a fish, or serpent. The most complete retelling of what was probably a more ancient legend, dates from the end of the 14th century and recounts how Melusina and her sisters were punished by their mother for imprisoning their father in a mountain as an act of revenge for his failure to keep his promise not to enter her chamber when she was giving birth or bathing her children. Melusina's singular punishment was for her
lower body to become that of a serpent - but only on Saturday.

Here Melusina is portrayed by the lithesome seventeen year old Sally Elisabeth Osteryd, born to a modest farming family and painted here by Wilhelmson when she was modelling at the Swedish royal academy of art. The young Count Rheinhold von Rosen (1894-1961), who was taking classes in painting and drawing at the academy, met and fell in love with her. They married, despite the initial disapproval of his family, and had five children of whom the second child, Elsa Marianne von Rosen (1924-2014) had a renowned career as a ballerina, choreographer and ballet director.

Carl Wilhem Wilhelmson apprenticed as a lithographer at Meyer & Köster in Gothenburg, whilst taking evening classes at the School of Design and Crafts . He went on to become a full time student to Carl Larsson at the Valand Academy. In 1888, on the recommendation of Larsson and his former employers, he was awarded a scholarship from the Kommerskollegium that enabled him to travel to Leipzig. While there, he worked for several notable lithography firms. Despite this, he remained undecided as to whether he should pursue a career in lithography or strike out on his own as an artist. By 1890, he had saved enough money to move to Paris.

In Paris, he worked as an advertising artist while taking classes from Paul Sérusier and Maurice Denis at the Académie Julian. He may also have studied, at least briefly, with Jules Lefebvre and Tony Robert-Fleury. In 1893, he visited Brittany and, in 1895, had a small showing at the Salon. He returned to Sweden in 1896.
Upon his return, the art patron, Pontus Fürstenberg, invited him to become the Director at the Valand Academy, where he accepted and held that position until 1910. After leaving the Academy, he opened his own art school. At the invitation of his friend, Hjalmar Lundbohm, he made expeditions to Norrland in 1914 and 1918 and produced several well known paintings in Bohuslän. He was appointed a Professor at the Royal Swedish Academy of Fine Arts in 1925 and became a member in 1926, in reverse of the usual order.

In addition to his canvases, he painted murals at the Dicksonska folkbiblioteket and the Central Post Office Building (Stockholm).