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Study and Revision of Archimedes (Hall)

Study and Revision of Archimedes (Hall)

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Authors: G.E. Condra and M.K. Elias

From the original abstract: Detailed morphologic and anatomic investigation indicates a compound nature of the fossil growth-form known as Archimedes. Archimedes screws usually develop upon the outer edges of Fenestella zoaria and are made of the extended coiled meshwork of thie Bryozoa encrusted in the axis of the coiling by a protean organism, apparently an epizoic alga related to living kelps. The two symbionts formed intimate bryozoan-algal consortium, seemingly beneficial for both. All species of Fenestella discovered as Archimedes symbionts were also found to form independent, noncoiled zoaria. Nine of such Fenestella species are newly described. In America, Archimedes ranges from Lower Devonian (Falls of Ohio River) to Lower Pennsylvanian (Utah) while in Russia it is found only in Upper Carboniferous and Lower Permian. In the Lower Devonian only the loosely coiled Archimedes (called Helicopora by Claypole) is known, while in the other, younger rocks both loosely coiled and tightly coiled zoaria, with heavy central screw, are well-represented. Coiling of Archimedes is believed due to growth in whirlpools originatng at proximal edge of some Fenestella colonies capable of producing food-bringing current. Only species of Fenestella with fine meshwork, having 2 to 3½ zooecia in fenestrule, produced tightly coiled Archimedes; species with coarser meshwork, 3 to 4 zooecia in fenstrule, produced lax Archimedes helicoids; and species with still coarser meshwork, over 4 zooecia in fenestrules, did not coil. The number of valid species, 13 of which are new, is: 1 (?) in Upper Silurian; 1 in Lower Devonian; 8 in Keokuk and Warsaw and 23 in Chester of Mississippian; 5 in American Lower Pennsylvanian; and 8 in Russian and Arctic Upper Carboniferous and Permian.

Published: 2/29/1944

ISBN Number: 9780813720531

Pages: 251

Product Category: EBooks