The Collaborative International Dictionary of English v.0.48:

Pecten \Pec"ten\, n. [L. pecten, -inis, a comb, a kind of
   shellfish. See Pectinate.]
   1. (Anat.)
      (a) A vascular pigmented membrane projecting into the
          vitreous humor within the globe of the eye in birds,
          and in many reptiles and fishes; -- also called
          marsupium.
      (b) The pubic bone.
          [1913 Webster]

   2. (Zool.) Any species of bivalve mollusks of the genus
      Pecten, and numerous allied genera (family
      Pectinid[ae]); a scallop. See Scallop.
      [1913 Webster]

   3. (Zool.) The comb of a scorpion. See Comb, 4
      (b) .
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

marsupium \mar*su"pi*um\, n.; pl. marsupia. [L., a pouch],
   (Anat. & Zool.)
   (a) The pouch, formed by a fold of the skin of the abdomen,
       in which marsupials carry their young; also, a pouch for
       similar use in other animals, as certain Crustacea.
   (b) The pecten in the eye of birds and reptiles. See
       Pecten.
       [1913 Webster]

WordNet (r) 3.0 (2006):

marsupium
    n 1: an external abdominal pouch in most marsupials where
         newborn offspring are suckled