Figure 64: Marginal cord in nummulitids.
A-B: Assilina ammonoides ( ), Recent, Gulf of Aqaba, Red Sea. SEM graphs after , 1977. A: Detail of marginal cord in a shell broken in the axial plane. Double arrow B - B indicates the approximate position of the cut in the cast of Fig. B. B: Detail of marginal cord in an epoxy resin cast that was cut approximately in the equatorial plane (as indicated in Fig. A), showing canal and chamber lumina after dissolution of shell. White arrows indicate direction of growth. C: Nummulitic limestone from Steinbach, Einsiedeln, Swiss Helvetic Alps, Lower Eocene (Cuisian). Transparent light micrograph of section perpendicular to bedding plane. 1: Assilina sp. of A. ammonea- praespira phyletic line, with particularly large and prominent marginal cord; 2: Nummulites spp.; 3: Assilina sp. of A. spira phyletic line; 4: Assilina sp. of A. exponens phyletic line; 5: Asterigerina cf. rotula ( ): no marginal cord.
ch: chamber lumen; isc: intraseptal canal system; mc: marginal cord; mcc: marginal cord canals; sf: septal flap; st: stolon; sulc: sulcus canal.