PTERIDOPHYTES. 518 PTEROPODA. 1895) • Atkinson, The Biology of Ferns (New York. ' 1804). For works on classification, see under Taxonoxt. ^^ t i. PTEBO DACTYL, tgr'A-dak'til (>eo-Lat., from Gk. nrtpiv, pleron, feather, wing + Si<rvo, dahlylos, finger). The common name for an> one of the flving lizards, remains of winch are found in the Mesozoic rocks There are about twenty different genera of pterodactyls all in- cluded in the order Pterosauria (winglizards). stretched along the sides of the body and sup- ported bv the fore and hind limbs and the tail. The structure of the fore limb is quite different, however, from that seen in bats and birds, and presents equally interesting modifications of the parts of the arm in the adaptation of the latter from a walking leg to a wing-like organ. The long bones are considerably lengthened, the first finger is sometimes represented by a sort of deT,v- claw. the second, third, and fourth fingers are small and slender and furnished with sharp- hooked claws, and the fifth, or 'little finger,' is greatly elongated and strengthened to form the framework along which the anterior edge of the wing membrane is attached. Impressions of these 1. Dimnrpl.odon raaorony^i ; 2. pteranodon. the toothless, bird-like type of jaws. also called Ornithosauria (bird-lizards) All the members of this order show a remarkable adapta- ti.m of the lizard body to bird-like habits, though in structure they remain essentially rep- tilian. They cannot be considered as ancestral to the birds, for they constitute a wholly yide- ,,endent line of descent, probably derived from common dinosaurian ancestors, and they present an instructive example of parallelism of ev(du- tion due to adoption by two separate races of similar modes of life. The pterodactyls have skeletons of light but firm construction with hollow bones. The earl- ier forms had strong, spreading teeth which gradually disappeared in successively later mem- bers of the group, and the loss of the teeth was .„„,„ accompanied bv a corre- PTERODACTYLIIS SPErXABILIS. } . ■ ■ s])onding increase m length and sharjiness of the jaws until in the latest genera (Pteranodon, etc.) the jaws are dagger-like. The large eyes, surrounded by a ring of sclerotic plates, are placed well back and on the sides of the skull. The body BBAMPHOBHYNCHUS OENrMisoi (lithographic stone ot Bavaria). was short and rather stout, the limbs long and slender, and in the earlier forms there was a long slender l^il. The wings resembled in gen- eral those of the bats rather than those of birds, for they consisted of thin but strong membranes wing membranes have in sev- eral cases been found so well preserved that the courses of the arteries are easily traceable. The hind limbs are of decidedly reptilian structure and from well-de- veloped organs of locomotion in the earlier members of the group, they degenerated PTERODACTYL OF THE to Weak chiwcd oi'gans of GEXU8 RHAMPHoRHYN- pyehcnsion bv which the cats (restored). {^^^^^ ^^^^^.^ j-j^j^j,^. ^^^^■._^^_ ized, pterodactyls probably suspended themselves from points of rocks or from the limbs of trees after the manner of the modern bats. The various genera range in size from less than 12 inches to about 20 feet in spread of wings. Some of them were evidently able to do little more than sail on leaping through the air, as does the flying squirjel. by means of the stretched membranes : while others were among the most powerful Hying creatures that have ever lived. The principal genera are Dimorphodon, Rhani- phorhynchus, Pterodactylus, and Pteranodon, or Ornitiiostoma. BiBLiOGKAPiiY. Von Zittel and Eastman. Tej-t- Book of Palceontology. vol. ii. (New York and London, 1902) : Voodward, Outlines of Terfe- hrate Paleroiitoloqy for ^tudriits of Zoology (Cambridge, 1898) : Seeley, The Ornithosauria (ib., 1890) ; id.. Dragons of the Air (London, 1901) ; Zittel. "Die I'Tiigsaurier aus dem Litho- graphischen Schiefer," PaUeontographica, vol. xxix. (Berlin, 1882); Williston, "Winged Rep- tiles." Popular Hcienee ilonthlg, vol. Ix. (New Y'ork. 1902) : Lucas. "The Greatest Flying Crea- ture, the Great Pterodactyl, Ornithostoma." Annual Rejiort of the f<mif'hsonian Institution for 1901 (Washington. 1902). PTEROPOBA (Neo-Lat. nom. pi., from Gk. vTepdirovs, pteropous. wing-footed, froin nTepin, pleron. feather, wing + iroiJs , pous, foot). An order of gastropod mollusks, agreeing in most of their features with the tectibranch forms like Bulla, etc. The head, eves, and tentacles are usually wanting or vestigial, while on each side of the mouth are wing-like appendages, appa- rently a pair of trreatlv developed parapndia, giving the peculiar 'butterfly' appearance to these' beautiful pelagic mollusks. The shell is conical or helix-like. The species are hernia-
