Dorsolateral Conotheca Phragmocone Diameter mm

Dorsolaterally (between 10 o'clock and 2 o'clock respectively on both sides of the conotheca), the most remarkable observation is the wedging out of the nacreous layer (Fig. 14.5A, B). At a distance of 200 |im, the nacreous layer thins out and disappears completely (Fig. 14.5B). Consequently, both inner and outer prisms merge together (25 ||m) and are no longer distinguishable. The laminar layer

Fig. 14.3 (A) Ventral cross-fracture of specimen MC-8 (phragmocone diameter = 10mm) to show inner prismatic layer (ipl), nacreous layer (nl), and rostrum (ro); 1,000x enlarged. (B) Detail of (A) to show nacreous layer (nl), outer prismatic layer (opl), lamellar layer (ll), and rostrum (ro); 3,000x enlarged.

Fig. 14.3 (A) Ventral cross-fracture of specimen MC-8 (phragmocone diameter = 10mm) to show inner prismatic layer (ipl), nacreous layer (nl), and rostrum (ro); 1,000x enlarged. (B) Detail of (A) to show nacreous layer (nl), outer prismatic layer (opl), lamellar layer (ll), and rostrum (ro); 3,000x enlarged.

between the rostrum and the now single inner prismatic layer is still present (2-3 |im). In some places (Fig. 14.5A), the inner surface of the rostrum displays similar borings as described in Doguzhaeva et al. (2003b), which indicate a high organic content. In other places, gaps are filled with secondary calcite (Fig. 14.5B).

Fig. 14.4 (A) Detail of Fig. 14.3B to show outer prismatic layer (opl), lamellar layer (ll), and rostrum (ro); 7,000x enlarged. (B) Lateral cross-fracture of specimen MC-8 (phragmocone diameter = 10mm) to show inner prismatic layer (ipl), nacreous layer (nl), and outer prismatic layer (opl). The lamellar layer (ll) is disintegrated; 3000x enlarged.

Fig. 14.4 (A) Detail of Fig. 14.3B to show outer prismatic layer (opl), lamellar layer (ll), and rostrum (ro); 7,000x enlarged. (B) Lateral cross-fracture of specimen MC-8 (phragmocone diameter = 10mm) to show inner prismatic layer (ipl), nacreous layer (nl), and outer prismatic layer (opl). The lamellar layer (ll) is disintegrated; 3000x enlarged.

Fig. 14.5 (A) Dorsolateral cross-fracture of specimen MC-8 (phragmocone diameter = 10mm) to show inner prismatic layer (ipl), thin nacreous layer (nl), outer prismatic layer, lamellar layer (ll), and inner surface of rostrum (ro). The lamellar layer is bored; 3,000x enlarged. (B) Dorsolateral cross-fracture (only 50]im dorsal from A). The nacreous layer wedged out. The lamellar layer is replaced by secondary calcite; 3,000x enlarged.

Fig. 14.5 (A) Dorsolateral cross-fracture of specimen MC-8 (phragmocone diameter = 10mm) to show inner prismatic layer (ipl), thin nacreous layer (nl), outer prismatic layer, lamellar layer (ll), and inner surface of rostrum (ro). The lamellar layer is bored; 3,000x enlarged. (B) Dorsolateral cross-fracture (only 50]im dorsal from A). The nacreous layer wedged out. The lamellar layer is replaced by secondary calcite; 3,000x enlarged.

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