Fig. 2 in Precursory siphuncular membranes in the body chamber of Phyllopachyceras and comparisons with other ammonoids

Fig. 2. Phyllopachyceras ezoense (Yokoyama, 1890). UMUT MM 28658 from the lower Campanian of the Nakanofutamata−zawa Creek, Haboro area, northwest Hokkaido (median longitudinal section). A. Occurrence of precursory siphuncular membranes in the rear part of the body chamber showing locations of photos B–D. B. Adoral end of the last septal neck, showing the outer conchiolin layer resting on the nacreous layer of the septal neck. C. Conchiolin membranes in the rear part of the body chamber, consisting of thinner inner and thicker outer layers. D. Adoral end of the conchiolin membranes in the body chamber, which consist only of the outer layer. Abbreviations: bc, body chamber; ic, inner conchiolin layer; n, nacreous layer of septal neck; s, septum; sn, septal neck; oc, outer conchiolin layer.