The Collaborative International Dictionary of English v.0.48:

Chelonia \Che*lo"ni*a\ (k[-e]*l[=o]"n[i^]*[.a]), n. pl. [NL.,
   fr. Gr. chelw`nh a tortoise.] (Zool.)
   An order of reptiles, including the tortoises and turtles,
   peculiar in having a part of the vertebr[ae], ribs, and
   sternum united with the dermal plates so as to form a firm
   shell. The jaws are covered by a horny beak. See Reptilia;
   also, Illust. in Appendix.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Chelonia
    n 1: green turtles [syn: Chelonia, genus Chelonia]
    2: tortoises and turtles [syn: Chelonia, order Chelonia,
       Testudinata, order Testudinata, Testudines, order
       Testudines]