The surrounding axial furrow is directed outward, than strongly bends backward and than curves regularly ever more inward. Over the posterior ⅔ of the rear part a strip about as wide as the node on the central part may be discernible, which ends in a node that at the very rear of the rhachis. The distance between the rhachis and the border furrow (or post axial length) is about equal to ¼ of the rhachis. The pygidial border is about ⅛ of the rhachis.
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A pair of small spines at the outer rear corners is present. The border furrow is wide. The rhachis has parallel sides or is conical, but the second segment is not narrower than its neighbours. Furrows crossing the rhachis are absent or weak.
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Opposite to the rear of the rhachis the border may carry a small spine at each side.
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Rhachis tulearensis is a species of conical air-breathing land snail, a gastropod mollusk in the family Cerastidae.
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Species with a rear rhachis lobe longer than the postaxial region are henceforth combined in Geragnostus, all others are assigned to Trinodus.
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The central raised area of the cephalon (or glabella) is outlined at the rear, narrow and tapering forward. It carries an elongated median node, clearly in the front half of the cephalon. The pygidial axis (or rhachis) is very broad, with the frontal lobe (M1) defined by a furrow crossing the axis. There is a weak elongated node on the rhachis.
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The short but wide triangular pygidium, with a rather low axis (or rhachis) of up to six indistinct rings that reaches the faint border furrow.
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The area outside the rhachis (or pleural zone) is usually smooth, and like on the cephalon, the border and border furrow are very narrow but distinct.
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Rhachis sanguineus is an extinct species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the superfamily Enoidea. This species was endemic to Mauritius.
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Catkins appearing with the leaves in April, terminal on very short, spreading, leafy, lateral shoots, peduncle and rhachis softly villose. Catkins male, female or most commonly androgynous.
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The segments are shown by differences in relief of the rhachis. There is a large median node, and a postaxial furrow is present, but usually very short.
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Rachis is a genus of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Cerastidae. This genus is also spelled as “Rhachis”as a synonym.
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The rhachis is about ⅓ of the pygidial width anteriorly, tapering evenly backwards. There is no pygidial border. There may be small spines extending from the frontal corners of the pygidium.
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Leaves are 140–180 cm long, flat in section (opposing pinnae inserted at 180 degrees on rhachis), with 130 -150 pinnae, terminated by a spine c. 4mm long; petiole usually glabrous, usually unarmed, rarely spinescent for up to 20% of length, 35 – 45 cm long; median pinnae at 70-80 degrees to rhachis, 240 – 280 mm long, 16 –17 mm wide, 0.35 - 0.45 mm thick, glabrous, dull green or slightly bluish-green when developing, becoming glossy mid-green at maturity, flat in section with slightly recurved margins, strongly discolorous, decurrent for 7–10 mm, narrowed to 5.0-6.0 mm at base, 17 – 20 mm apart on rhachis apex attenuate; midrib not sharply raised, more or less equally prominent above and below, 1.2 -1.5 mm wide.
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Rhachis comorensis is an extinct species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the superfamily Enoidea. This species was endemic to Mayotte, an island in the Indian Ocean.
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This agnostoid is strongly effaced. The cephalon lacks a border furrow. The glabella and small basal lobes are weakly defined. The rhachis is circular to ovate, clearly defined by deep axial furrows.
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Free cheeks are rarely present. Dorsal sutures are proparian. The pygidium is subcircular, about 1⅔× as wide as long. The segmentation of the pygidial axis (or rhachis) and pleura is indiscernible or very weak.
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Whittington, H. B. et al. (1997) Treatise on Invertebrate Paleontology. Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. Also the axis (or rhachis) and pleural fields of the pygidium are strongly segmented.
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The free cheeks (or librigenae) are long. The thorax has three segments. The tailshield (or pygidium) has a long axis of 10 almost indiscernible rings. The furrow that defines the axis in the pygidium (or rhachis) is almost obsolete.
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The central part of the inflorescence axis is long. It also has angular rhachis which bottom is glabrous. The spikelets grow in pairs and are apart from each other. They are also fertile, pedicelled, and sessile, with pedicels being oblong.
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Pacay is a medium to large sized tree up to tall. Indumentum of pubescent hairs with rusty color on young branchlets, leaf rhachis and inflorescences. Leaves have 3-5 pairs of oblong- elliptic leaflets, with a terminal leaflet of ca. 10–20 cm long.
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The pygidial axis (or rhachis) is – times as long as the pygidium, almost parallel-sided, very slightly constricted at the middle lobe (M2), broadly rounded, and – times as long as wide. It has three distinct pairs of lobes, and is defined by shallow furrows. The forward lobe of the rhachis (M1) is a bit shorter and wider than the middle lobe (M2) and separated from it by a furrow (F1) which is directed outward and slightly backward from the dorsal furrow, and then curved strongly forward adaxially. The rear lobe (M3) is – longer than both others together, and the furrow is directed outward and slightly forward from the dorsal furrow.
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It is borne on a side of central axis, is unilateral and is long. The central inflorescence axis long with angular rhachis and is either glabrous or pilose on the bottom. Spikelets come in 2 rows which are fertile, pedicelled, and sessile. The pedicels are oblong.
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The occipital ring may be simple or split into two lateral lobes (in Chelediscus and Tannudiscus). All Weymouthiidae lack eyes. The articulate middle part (or thorax) consists of three rings when known (Mallagnostus, Marocconus, Serrodiscus, Tannudiscus and Weymouthia). The tailshield (or pygidium) has a long, strongly tapering axis (or rhachis) with 10 or more rings.
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The family name Rachycentridae, from the Greek words rhachis ("spine") and kentron ("sting"), was inspired by these dorsal spines. The mature cobia has a forked, slightly lunated tail, which is usually dark brown. The fish lacks a swim bladder. The juvenile cobia is patterned with conspicuous bands of black and white and has a rounded tail.
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The posterior part of the glabella is large and carries an inflated spine that is directed upwards and backwards. Genal spines are present. The axis of the pygidium (or rhachis) has nine rings that are strongly inflated, with the second ring carrying a vertical spine. The border surrounding the pygidium is defined by a deep furrow, is narrow, and lacks spines.
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Geragnostus is very similar to Trinodus and may in future be included in that genus. In Trinodus the posterior lobe (M3) of the pygidial axis (or rhachis) is clearly shorter than the anterior and middle lobes (M1+M2) combined, while in Geragnostus it is equal or greater in length. Geragnostus is not closely related to Micragnostus, because its glabella is structurally different.
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The palpebral lobes are short but prominently raised, and the librigenae tiny. The anterior border usually is a short rim marginal to a long border furrow. The pygidium has a rhachis of six or seven rings and tiny terminal portion, with a small tubercle on each ring, and without a terminal spine. The pleural areas usually with well impressed pleural furrows.
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These animals, up to nine centimeters long, had an oval outline and a strongly arched exoskeleton. The cephalon has a smooth, detail-poor surface and an almost inconspicuous occipital bone behind the glabella in the transition to the thorax. The facet eyes have crescent-shaped lids. The thorax consists of ten narrow segments and a clearly arched and broad axial lobe ( rhachis ).
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Engelhardia serrata is a tree growing up to 12 m tall. The leaves are pinnate, rarely unpaired, and 150–250 mm long. The petiole is 10–20 mm long and hairy; the rhachis is also hairy. The 6 to 14 leaflets are seated or short stalked, the blade is elliptic to elliptic-lanceolate, 60–130 mm long and 25–45 mm wide, the underside is hairy.
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In Acmarhachis the furrow at midline between the front of the glabella and the border is weak or absent. The glabella has a long ogival to subquadrate front lobe, and the furrow defining it at its back is straight. The back lobe of the glabella is accompanied by two triangular basal lobes of moderate to large size. On the pygidium the axis or rhachis reaches the border.
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Lotus glaucus is a perennial herbaceous plant, usually forming dense mats, but sometimes somewhat shrubby. The leaves are unstalked (sessile) with five pinnate leaflets. In L. glaucus subsp. glaucus, the two basal leaflets are 1.5–4.5 mm long; a short axis (rhachis), up to 2 mm long, separates the basal leaflets from the other three leaflets, which are 2–8 mm long, longer than the basal leaflets.
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The fruit is a red hip 1–2 cm diameter. The strong, stalk-round branches have an almost bare, purplish-brown bark and there may be many to no curved, stocky, flat spines. The alternately arranged leaves are divided into petiole and leaf blade and a total of 5 to 11 inches long. The petiole and the rhachis are sparsely spiked and glandular-fluffy hairy.
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Rhacophytales are an extinct group of plants from the Devonian period. The representatives are characterized by a unique branching system in which bi- and quadriseriate units occur which are located in the axils of special structures, the aphlebiae. These are abnormal leaflets on the rhachis of ferns. The appendages of the last branching stage can be dichotomously branched, in some forms they stand in one plane.
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Lotus tenellus is a perennial herbaceous or shrubby plant. The leaves are either unstalked (sessile) or have a very short petiole, and are made up of five pinnate leaflets. The two basal leaflets are 1–5 mm long. A short axis (rhachis) 1–2 mm long, shorter than the basal leaflets, separates them from the other three leaflets, which are 2–7 mm long, usually longer than the basal leaflets.
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There is a furrow at midline connecting the glabella with the border furrow. The axis of the pygidium (or rhachis) has three sections. The frontal section is split into three parts. Both lateral parts are defined by furrows on all sides: those with the central section directed backward and very slightly outward, those with the middle section outward and slightly backward, and those with the pleural zone backward and slightly inward.
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However abortion rates are difficult to assess because the ovaries are deeply embedded in the "rhachis" (woody spine) of the inflorescence. Finally, there is the mechanism of "facultative" abortion of fruits, where a maternal plant without the resources to mature all fruit aborts the least vigorous ones. This is thought to be common in those taxa that are generally self-compatible, since even these have high outcrossing rates. For example, Banksia spinulosa var.
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The pygidial axis (or rhachis) is not connected to the border by a median (postaxial ) furrow. The pygidium carries backward directed spines on its margins, where it curves back towards the midline. In the subgenus Agnostus (Agnostus), the axis of the pygidium is relatively narrow, ending pointed, or narrowly rounded, and furrows crossing the pygidial axis are weak at best. The subgenus Agnostus (Homagnostus) has a broadly rounded termination of the axis extending nearly to posterior border furrow.
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Astreptorhachis is an extinct genus of Late Carboniferous dissorophoid temnospondyl within the family Dissorophidae. It is known only from one species, Astreptorhachis ohioensis, that was collected from Jefferson County, Ohio by the Ohio Geological Survey in 1953 and described by Peter Vaughn in 1971. The holotype and only known specimen consists of a few neural spines and is currently reposited in the Smithsonian Museum of Natural History. The genus name derives from the Greek words astreptos ("inflexible") and rhachis ("backbone").
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Rachischisis (Greek: "rhachis - ῥάχις" - spine, and "schisis - σχίσις" - split) is a developmental birth defect involving the neural tube. This anomaly occurs in utero, when the posterior neuropore of the neural tube fails to close by the 27th intrauterine day. As a consequence the vertebrae overlying the open portion of the spinal cord do not fully form and remain unfused and open, leaving the spinal cord exposed. Patients with rachischisis have motor and sensory deficits, chronic infections, and disturbances in bladder function.
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Phalagnostus is a genus of small trilobites, in the order Agnostida. It lived during the Middle Cambrian, in what are now Canada (Newfoundland and Northwest Territories), China, the Czech Republic, Denmark, England, France, the Russian Federation (Bennett Island, Yakutia), Wales, Sweden, and possibly the United States (Vermont). The headshield (or cephalon) is almost entirely effaced and wider than the tailshield (or pygidium). The pygidium is also very effaced, but the ovate pygidial axis (or rhachis) is well defined and a border furrow is also present.
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Ovatoryctocara is a genus of small corynexochid trilobites from the Cambrian, that lived in what now are Siberia, China, Greenland and Canada (Newfoundland). Ovatoryctocara can be recognised by the combination of the following characters: the central raised area of the cephalon (or glabella) is approximately cylindrical and has two rows of four triangular or round pits. The thorax only has 5 or 6 segments. The tailshield (or pygidium) has an axis (or rhachis) of 6 to 12 rings, the pleural furrows are well developed and the border is absent or narrow as a hair.
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Ceroxylon vogelianum is a small to medium-sized palm with a stem of 3–17 meters tall and 12–25 cm in diameter. The crown can have 6 to 18 leaves, most of them almost upright or horizontally arranged. Leaf blades are made of 46–129 leaflets in a rhachis of 38–210 cm long; petiole 15–75 cm long. Male inflorescences around 160 cm long, with about 40 branches; male flowers with 6 stamens, with filaments up to 1.5 mm long and anthers 1.6–2.5 mm long.
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