Found by serendipity, this painting by Baldassare [di Matteo] Carari [1460–1516] in Walters Art Gallery is described as “The subject of this painting is the celebration of Christ’s birth, although the infant Christ, who stands in his mother’s lap, seems much older than a newborn. The ass and ox on the left are traditional witnesses of Christ’s birth in the Bethlehem stable. The procession in the background signals a later event: the arrival of the wise men from the East to pay homage to the Messiah. The painting is spectacular for its many plant and animal details, each with a specific symbolic significance. For instance, the snail (in the right corner) was often meant to suggest sin because of its trail of slime, and the red poppy (the second flowering plant on the left) is a traditional symbol of Christ’s Passion because of its color.” .
It may be noted, though, that the snail could also symbolise Mary’s virginity . The painting originated ca. 1485 in either Ravenna or Forli in Italy . See also item #19 for an iconographic similarity.
In the lower right-hand corner of this painting, a snail is climbing up a step. Although the snail is fairly realistically painted, precise identification is prohibited; it may be a Helix like species.
 WAG 37546. http://bit.ly/1bQ9XDE.
 Dittrich, S. & Dittrich, L. (2004). Lexikon der Tiersymbole. Tiere als Sinnbilder in der Malerei des 14.–17. Jahrhunderts. Imhof, Petersberg, 672 pp. See p. 460–468.