Fig. 5 in Precursory siphuncular membranes in the body chamber of Phyllopachyceras and comparisons with other ammonoids

Fig. 5. Phyllopachyceras ezoense (Yokoyama, 1890). UMUT MM 28660. Same specimen as that in Fig. 4. A. Siphuncular tube at the beginning of the second whorl, consisting of inner and outer conchiolin layers. The ventral side is distinctly detached from the ventral shell wall at this stage. B. Closeup of the ventral side of the siphuncular tube in the third whorl, showing that the membranes branching from the outer layer are attached to the ventral shell wall. Abbreviations: ic, inner conchiolin layer; oc, outer conchiolin layer; s, septum; vw, ventral shell wall.