\Si*re"ni*a\, n. pl. [NL.] (Zo["o]l.)
An order of large aquatic herbivorous mammals, including the
manatee, dugong, rytina, and several fossil genera.
Note: The hind limbs are either rudimentary or wanting, and
      the front ones are changed to paddles. They have horny
      plates on the front part of the jaws, and usually
      flat-crowned molar teeth. The stomach is complex and
      the intestine long, as in other herbivorous mammals.
      See {Cetacea}
(b) .