The Book of Hours of Emperor Maximilian I has a long and intriguing history. It has been described in detail by Walter L. Strauss , and for the full details one should consult his book.
Part of the illustrations have been made by Albrecht Dürer (1471–1528), among other things engraver who is famous for his many prints .
In the context of this blog, the page of interest is this one:
In the lower left corner an angel playing the lute is shown, with its (his/her) left foot on top of the shell of a snail, seen in side view from the right. While the animal is quite naturalistically drawn, the dextral shell seems stylised and may have been modelled after an imaginary species.
See also item #52, for which Dürer’s picture is assumed to have been inspirational.
 Strauss, W.L. (1974). The Book of Hours of Emperor Maximilian the First, decorated by Albrecht Dürer, Hans Baldung Grien, Hans Burgkmair the Elder, Jörg Breu, Albrecht Altdorfer, and other artists. Printed in 1513 by Johannes Schoensperger at Augsburg. Abaris Books, New York, 344 pp.