Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . ontogenetic development, changing from prominently trituberculate throughquadrituberculate to pentatuberculate. The authors are not entirely sure that their interpretation of the species iswholly correct, due to great differences in size between the Madagascar andZululand specimens. It is not clear from Besairies (1930: 638) or CoUignons(1948: 26-27,1970: 54) descriptions of M. {A.) australis whether these specimensare still septate, or adult. The Madagascar specimens, if adults, are all verysmall, c. 80 mm-150 mm in
Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum . ontogenetic development, changing from prominently trituberculate throughquadrituberculate to pentatuberculate. The authors are not entirely sure that their interpretation of the species iswholly correct, due to great differences in size between the Madagascar andZululand specimens. It is not clear from Besairies (1930: 638) or CoUignons(1948: 26-27,1970: 54) descriptions of M. {A.) australis whether these specimensare still septate, or adult. The Madagascar specimens, if adults, are all verysmall, c. 80 mm-150 mm in diameter, when compared to the Zululand speci-mens, which are still septate at diameters in excess of 300 mm. The inner whorlsof the Zululand specimens, with depressed, subrectangular whorl section andenormous ventrolateral spines are, however, like typical Madagascar M. {A.)australis. This raises the question of whether Madagascar M. {A.) australiswhich are, in fact, trituberculate throughout, have arisen caenogenetically from 296 ANNALS OF THE SOUTH AFRICAN MUSEUM «#!^. Fig. 222. Menabites {Australiella) australis (Besairie, 1930). preceding that of Figure 223. x 1. a population similar to the much larger Zululand material, or whether thisSpecies has been interpreted only in terms of incomplete material in Mada-gascar. The holotype of M. {A.) australis, according to Besairies figures,measures about 150 mm in diameter. None of the Zululand specimens is stillunequivocally trituberculate at that diameter, although specimens such asNMB-D1336 (Fig. 229), with a very indistinct fourth row of tubercles, arevery close to the holotype. Besairie (1930: 638) had referred to the Zululandmaterial as Mortoniceras cf. australis, stating that it differed from M. australisonly by the possession of a doubled row of tubercles in lieu of a single row. In view of the normal wide range of intraspecific variation in the Texani-tinae, it is probably correct to refer the Zululand ma
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Keywords: ., bookcentury1800, bookdecade1890, booki, booksubjectnaturalhistory
