This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Siren (Greek)
In Greek mythology, sirens are humanlike beings with alluring voices; they appear in a scene in the Odyssey in which Odysseus saves his crew's lives. Roman poets place them on some small islands called Sirenum scopuli. In some later, rationalized traditions, the literal geography of the "flowery" island of Anthemoessa, or Anthemusa, is fixed: sometimes on Cape Pelorum and at others in the islands known as the Sirenuse, near Paestum, or in Capreae. All such locations were surrounded by cliffs and rocks.
The sirens of Greek mythology first appeared in Homer's Odyssey, where Homer did not provide any physical descriptions, and their visual appearance was left to the readers' imagination. It was Apollonius of Rhodes in Argonautica (3rd century BC) who described the sirens in writing as part woman and part bird. By the 7th century BC, sirens were regularly depicted in art as human-headed birds.