The Collaborative International Dictionary of English v.0.48:

Pentail \Pen"tail`\, n. (Zool.)
   A peculiar insectivore (Ptilocercus Lowii) of Borneo; -- so
   called from its very long, quill-shaped tail, which is scaly
   at the base and plumose at the tip.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pen-tail
    n 1: brown tree shrew having a naked tail bilaterally fringed
         with long stiff hairs on the distal third; of Malaysia
         [syn: pentail, pen-tail, pen-tailed tree shrew]