Figure 20 in Phylogeny of cardiid bivalves (cockles and giant clams): revision of the Cardiinae and the importance of fossils in explaining disjunct biogeographical distributions

Figure 20. Spines of Afrocardium exochum (ANSP 293709). A, radial section through central portion of a rib to illustrate shell microstructure. Direction of ventral margin to left, direction of umbo to right. B, SEM of detail of exterior of right valve. Note alternation of one wider rib covered with larger triangular spines with one narrower rib covered with smaller triangular spines. C, SEM of dorsal view of right valve. Again, note alternating rib width and spine strength. Scale bars: A = 0.1 mm; B, C = 0.2 mm.