THE ORIGIN OF THE FAMILY HORRIDONIIDAE MUIR-WOOD ET COOPER |
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| Abstract: | The late Paleozoic genus Praehorridonia and its type species is described, differing from Horridonia by presence of radial and concentric sculpture and by absence of spines on the brachial valve. The author believes the large Praehorridonia possessing traces of semireticulate structure, descended from the strongly semireticulate Antiquatonia in Middle Carboniferous and evolved into Horridonia, thus representing an intermediate stage between Antiquatonia and Horridonia. The family was confined to the Arctic throughout its history and became extinct in the middle of the Upper Permian. -- G. A. Cooper. |
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