Fig. 4 in Precursory siphuncular membranes in the body chamber of Phyllopachyceras and comparisons with other ammonoids

Fig. 4. Phyllopachyceras ezoense (Yokoyama, 1890). UMUT MM 28660 from the middle Campanian of the southern tributary in the Osousyunai Creek, Nakagawa area, northern Hokkaido (dorso−ventral cross section). A. Ventral side of the body chamber, showing the shape of the precursory siphuncular membranes that directly contact the outer shell wall and the locations of photos B–D. B–D. Precursory siphuncular membranes at the dorsal (B), ventrolateral (C) and ventral (D) sides. At every side, the membranes are made up of a thinner homogeneous inner layer and a thicker outer layer with pillar−like units. Abbreviations: bc, body chamber; ic, inner conchiolin layer; oc, outer conchiolin layer.