Fig. 3 in Precursory siphuncular membranes in the body chamber of Phyllopachyceras and comparisons with other ammonoids

Fig. 3. Phyllopachyceras ezoense (Yokoyama, 1890). UMUT MM 28659 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 location of photos B, C. The membranes have a length equivalent to that of the two last camerae. B, C. Anterior end and close−up of the conchiolin membranes. The inner layer disappears just before the adoral end, whereas the outer layer still exists. Abbreviations: bc, body chamber; ic, inner conchiolin layer; n, nacreous layer of septal neck; oc, outer conchiolin layer; s, septum; sn, septal neck.