Morphometric analysis was performed on 19 adult specimens from AMT20 and AMT24 and from the recent fossil record of site CAR-MON 2 (Le Friant et al., 2008; Wall-Palmer et al., 2014). Images of the apical side of each shell were obtained using light microscopy and scanning electron microscopy. The ImageJ software FIJI (Schindelin et al., 2012) was used to measure the shell diameter perpendicular to the nucleus of the protoconch (Fig. 2) at half whorl intervals throughout each shell.
Fig. 2. Method of whorl counting of Protatlanta shells, following the method of whorl numbering by Seapy (1990) and morphometric shell measurements for P. souleyeti (black circles, black lines) and P. sculpta (white triangles, grey lines) shells. For specimens analysed, see supplementary Table S1. Specimen used for method schematic is P. sculpta from Figure 3k.