Fig. 4 in Lower Tithonian microconchiate simoceratins from eastern Mexico: Taxonomy, biostratigraphy, and palaeobiogeography

Fig. 4. Simoceratin ammonoid Pseudovolanoceras aesinense chignahuapense (Cantú−Chapa, 1990) [microconch]. A–F. From the Apulco section (MT−2). A. Right−side view of IGM 6085−2a showing lappet, bed 21b. B. Right−side view of IGM 9541; eroded and slightly distorted specimen, bed 21b. C. IGM 9543a, close−up view showing incipient longitudinal furrow between tubercles (C1) (see text for allusion to "cordone spirale"); right−side view (C2), bed 25. D, E. IGM 9546a and b, both from the same flattened inner mould. D. Imprint of the left side. E. Left−side view; arrows for lappet and tubercles showing riblets, bed 25. F. Left−side view of IGM 9542a, bed 21b. G. IGM 9544; G1, right−side view, arrow showing the last suture line preserved; G2, close−up view from the body chamber showing tubercles with riblets (arrows); G3, ventral view showing longitudinal furrow between tubercles, arrows indicate the trace of the "cordone spirale" (see text for allusion to "cordone spirale"); G4, close−up view of inner whorls showing tubercles with riblets (arrows); from MTQ section, bed 11.