Trocholitoceras juvenicostatum Ulrich, Foerste, Miller & Furnish 1942

• Main Authors: Kröger, Björn, Pohle, Alexander
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2021
• Subjects: Biodiversity; Taxonomy; Animalia; Mollusca; Cephalopoda; Tarphycerida; Trocholitidae; Trocholitoceras; Trocholitoceras juvenicostatum; Ny Friesland; Svalbard
• Online Access: https://doi.org/10.5281/zenodo.5795821; http://treatment.plazi.org/id/5F4487ACFFE9FFE9FEB97BE1FDEA795D

Trocholitoceras juvenicostatum Ulrich, Foerste, Miller & Furnish, 1942 Figs 44C, 48 Trocholitoceras juvenicostatum Ulrich, Foerste, Miller & Furnish, 1942: 82, pl. 51 fig. 6, pl. 53 figs 5–6, pl. 56 figs 1–3. Diagnosis Trocholitoceras with relatively narrow whorls and prominent ribs throughout entire growth; sutures directly transverse with dorsal lobe; siphuncle located close to the dorsal wall in mature portions of the phragmocone (compiled from Ulrich et al. 1942: 82). Material examined Six specimens (FMNH-P30323, P30324, P30330, P30332, P30344, P30347), all from Profilstranda section, Ny Friesland, Svalbard, bed PO 131, 128 m above base of Olenidsletta Member, Blackhillsian, Floian. Description Specimen FMNH-P30323 (Fig. 48A–B) is the most complete specimen assigned this species; it is a fragment of a phragmocone, which is partly heavily recrystallized and part of a 140° long continuously growing body chamber, and which grows with a WER of 2.03. At the base of the body chamber the conch diameter is 37 mm and the whorl is 16.5 mm wide and 11 mm high (rW = 1.05). The slightly depressed cross section has flattened flanks, a rounded venter and a shallow imprint zone (0.6 mm at whorl height 11 mm) (Fig. 44C). The conch is ornamented with prominent ribs which run obliquely transverse across the whorl and form a deep hyponomic sinus over the venter; ca 20 ribs occur per volution and the distance of the ribs is ca 4 mm at the base of the body chamber. Additionally, the conch surface is finely striated with ca 5 striae per mm, which run parallel to the ribs. The annulation appears to be constant in amplitude and relative spacing over the entire preserved part of the specimen. On the imprint of the inner shell a wrinkle layer is visible (Fig. 48A). The septal perforation is ca 2.9 mm in diameter and positioned sub-dorsally, ca 1.5 mm from the dorsum at the base of the body chamber. The chamber distance is visible in specimen FMNH-P30324, which is a small fragment of a phragmocone with a conch diameter of 22 ...