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Species / Monalaria Poliveta


Original Description of Monalaria poliveta by J.D. Stilwell, 2000:

  • "Shell quite small for family (height 20 mm), rather thin-shelled, elongate subovate in outline; ratio of height of shell to diameter of last whorl ca 1.3:1; spire moderately high of at least 4 convex, weakly shouldered whorls with shoulder located at mid-height; protoconch unknown but apparently paucispiral and minute; teleoconch of some four rapidly expanding whorls; greatest whorl inflation from penultimate to last whorl; spire angle approximately 76º; suture weakly impressed to slightly canaliculate and declivous; last whorl strongly inflated, bicarinate, adapical slope markedly steep, short, and mostly flat except at intersection of strong keel where it is weakly concave; adapical keel ca 1.5-2 mm wide, positioned a quarter of the height of last whorl from suture; central portion of last whorl concave demarcating adapical and abapical keels, latter much more weakly developed than the former and located ca 3 mm from adapical keel at onset of strong basal constriction which yields markedly excavated profile; last whorl highly but finely ornamented with predominantly spiral sculpture of more than 30 variable and rather weak spiral cords, those on shoulder finer and more bunched than those below, becoming more prominent at shoulder angulation, bearing approximately 32 poorly developed opisthocline tubercles, then becoming more spaced and weaker at concavity abapical of shoulder angulation, then strengthening again at lower angulation where cords broaden and weaken again at onset of canal; some interstitial threads present between primary cords; axial sculpture weak, of sinuous, opisthocyrt-trending growth lines on shoulder, becoming opisthocline abapically; posterior or adapical sinus angle ca 47º; intersection of spiral cords and growth lines forming a somewhat cancellate pattern on lower third of last whorl, especially; penultimate whorl sculpture of five equally spaced spiral cords and weak opisthocline growth lines with quite weak shoulder tubercles demarcating weak peripheral angulation; early teleoconch whorls with spiral sculpture only; holotype (adult) with one previous sinuous varix, retained during later growth; aperture subovate to sublenticular; inner lip with thin parietal callus; columella partially obscured by fine matrix, but apparently rather short and straight; outer lip with prominent, rather narrow, sinuous varix, markedly opisthocline from angulation on penultimate whorl to lower abapical angulation, becoming slightly orthocline or convex with moderately broad, but shallow, very gently twisted siphonal canal; labrum smooth."

Locus typicus: Waihao River bed 200 m upstream from “Corrody” homestead, Waihao River, South Canterbury, South Island, New Zealand.

Stratum typicum: Five Forks Glauconitic Sands Member of Kauru Formation, Mangaorapan (Dm) to Heretaungan (Dh) Stages (Dannevirke Series), late early to early middle Eocene


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