PTARMIGAN. 51G PTARMIGAN (with inorganic initial p.frova Gael, liir.iniihan, Iv. tarmocliun, tiirmonach, ptarmigan). A kind of grouse, differing from true grouse (q.v. ) eliielly in having the tarsi and toes thiel<l.v clothed with sliort feathers. The species are "natives of northern or greatly elevated regions. They are not polygamous like the true grouse, nor do the males strut with erected and expanded tail. Most of the species change color on the approach of winter, assuming at the fall molt a white or nearly white plumage, in place of the mottled reddish brown of summer. At this season also the shanks and feet acquire longer PTERIDOPHYTES. SEASONAL CHANGE IN PTAHMIGAN 8 CLAWS. B, .summer condition : foot of willow ptarniig'an, drawn June 10. just before the change to the short, summer claw ; Tf, winter condition : the same, drawn October 18, showing full-feathered preparation for winter. and denser feathering, and the sliort summer claws are shed and replaced by a growth of longer stronger claws of service in scratching away the snow to get at buried food; and the diversities of color have caused much confusion and difh- culty concerning them. All are highly esteemed as food, and are valued as game-birds. Less often seen in Great Britain, but widespread, and numerous in (Scandinavia and Northern Russia, whence great numbers are sent to market in win- ter, is a grayer species (Layojnis mill us). Two closely allied species, the 'rock' and the 'willow' ptarmigans, range throughout Arctic America, but do not extend southward to the United States. Along the summits of the Eockj' Mountains is to be found another species {Laf/optis leiicurus) in which the tail remains white all the year round, and it is therefore called the white-tailed ptar- migan, or "mountain quail.' All make their nests on the groyuid among the heather or thickets in which they pass their lives and find their food (buds, berries, leaves, and insects) , and lay brown eggs very heavily blotched with brownisli black. For bibliography, see Grouse. See Plate of Grouse, etc. ; and of Eggs of Water and Game Birds. PTERANODON, ter-an'6-d6n (Neo-Lat., from Gk. impbv, pteron, feather, wing -)- d>'65oi't, anodous, toothless, from dx-, oh-, negative prefix 4- (55oi/s, odoiis, tooth). A large fossil flying lizard, in fact the greatest known ilying creature; found in the Cretaceous rocks of Kansas. See Pterodactyl. PTERASPIS, t&r-a.s'pls (Neo-Lat., from Gk. TTTtpbv, pt(ron, feather, wing -- aairli, aspis, sliield). One of the most primitive fossil fishes of the subclass Ostracodermi, found in the Silu- rian and Devonian rocks. The front part of the body was covered by dorsal and ventral shields which were made up of several heavy bony plates united by fusion of their joints. The orbits are small and are placed well forward at the very margin of the head shield. The general form of the body was shark-like, its length about four or five inches: the posterior portion was covered by .small polygonal scales. See Ostracodermi. PTERICHTHYS, ter-ik'thls (Xeo-Lat., from Gk. TTTepiv, pirron, feather, wing + ix^is, ichthys, fish). A genus of ])rimitive fossil fishes of the .subclass Ostracodermi, found in Devonian rocks in (ircat Britain and Germany. The body was from four to eight inches long, broad and high in front, with flattened ventral surface and short tapering tail. The anterior portion is inclosed in large turberculated bony plates which are firmly united to each other, those of the head shield being articulated bj' a hinge with those of the body shield. The orbits are placed near together on the forward slope of the head and are separated by a small plate which has on its under surface a pit for the pineal body. A cleft between the lower margin of the head shield and the front nuirgin of the ventral body shield represents the mouth, and there have been found in- distinct traces of bones that are supposed to represent the jaws. At the sides of the front of the body shield are attached two paddle- shaped jointed appendages made up of small closely fitted plates, which resenfl)le the pectoral fins of the fishes. The tail portion, which is shorter than the armored portion of the trunk, is covered by small rounded or hexagonal scales, and has a small triangular dorsal fin and an upturned tip on the ventral side of which is a small caudal fin. A close ally of Fteriehthys is Bothriolepis, found in the Upper Deronian of North America and Europe. See Ostracodermi. PTERIDOPHYTES, ter'id-6-fIts (Neo-Lat. noiu. pi., from Gk. Trrepij, pterin, fern + ijivriv, phi/Ion. plant). The fern-plants, one of the four great divisions of the plant kingdom, ne.xt in order of rank to the highest group, the flowering or seed plants (spcrmatophytes) . There are tliree great divisions of pteridophytes : (1) ferns (Fili- cales), ('2) horsetails ( Equisetales) , and (.3) club-mosses (L.ycopodiales) . The pteridophyte- have a well-developed vascular system, which is entirely absent in the bryophytes, the next group Fig. 1. STRUCTURE OF A FERN. 1, diagrammatic section showing young sporophyte (shaded) in relation to prothallium ; 2. section of an arch- egonium : 3, section of an antheridiuin : i, sperm; 5, sec- tion of two 9ori, showing sporangia and indusium. below them. This system of conducting and strengthening tissues is correlated with the at- tainment of much greater size and larger foliage display by the fern plants than by the moss plants. It as.sociates them with the seed plants ( spcrmatophytes ) . Since plants below the seed
