. Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum. THE UNIONACEA OF SOUTH-CENTRAL AFRICA 157 in the adult stage and with sculpture over much of the shell, occurs in the Okavango River and its delta, and in the Linyanti swamp. This latter form, according to Mandahl-Barth (in litt. 13 October 1976), corresponds to typical C. kunenensis. An apparently intermediate form occurs in the Zambezi River at Katima Mulilo, the Okavango River and Ekuma floodplain. Shells referable to Nodularia croninae are known from the upper reaches of the Zambezi in eastern Zambia. Figure 3 sho
. Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum. THE UNIONACEA OF SOUTH-CENTRAL AFRICA 157 in the adult stage and with sculpture over much of the shell, occurs in the Okavango River and its delta, and in the Linyanti swamp. This latter form, according to Mandahl-Barth (in litt. 13 October 1976), corresponds to typical C. kunenensis. An apparently intermediate form occurs in the Zambezi River at Katima Mulilo, the Okavango River and Ekuma floodplain. Shells referable to Nodularia croninae are known from the upper reaches of the Zambezi in eastern Zambia. Figure 3 shows a significant difference (p < 0,01) between the shapes (as indicated by L/H v. length) of the Zambezi form and typical C. kunenensis, particularly amongst larger specimens. There is no meaningful difference in shell width relative to length and these dimensions are not shown. The measurements given by Dartevelle (1939) for five specimens of C. kunenensis from the upper Kunene (no precise locality given) indicate that these should belong to the typical form. Juveniles up to approximately 34 x 23 mm may be sculptured over the whole shell surface. In larger shells the sculpturing persists posteriorly and anteriorly, although specimens corresponding to N. croninae are generally smoother than the more southerly forms. Juveniles of the Zambezi form are usually green- yellow. The very small valves from the Kafue River (NM-A5366) are dominated by rugose and sometimes lamellate zigzag sculpture over the whole shell surface. Nothing is known of the nature of the localities where shells corresponding to N. croninae were found, but the Zambezi form and typical C. kunenensis may represent adaptations to fundamentally different environmental conditions. The present data indicate that the former occurs in lotic environments (perennial, flowing rivers) whereas the latter is found in lentic and often seasonally inundated areas. G. Mandahl-Barth has suggested (in litt. 13 October 1976) tha
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Keywords: ., bookauthorsouthafr, bookcentury1800, bookdecade1890, bookyear1898
