FIGURE 3 in The tube of Ditrupa bartonensis (Annelida, Serpulidae), from the Eocene of southern England: Observations on microstructure and its significance

FIGURE 3. Scanning electron images of the upper structural layer from Ditrupa bartonensis. A)-D) Longitudinal views of ridged crystals. Arrows indicate locations where cleavage planes are observed (approximately perpendicular to crystal long axis) – interpreted as growth lines in Vinn et al. (2008c). Areas marked with asterisk (*) are transverse cross-sections with conchoidal fracture. In (B) area within {} is possible remnants of organic framework / membrane, expanded in (D). 1-4 in (B) highly inclined fracture packets (also see Figure 5).