. Bulletins of American paleontology. Australian carpoids: Gill and Caster 53 considerably shallower than in V. ici/k/z/s/, , and the carapace may be much less hooded over this area than in the Heathcote material. Charac- teristic undulatory prosopon lines are present on the posterior half of the plastron. The specimen is notable for the presence of both brachial spines, affixed (ball and socket articulation) at the distal lateral extremities of the theca. The better preserved exothecal appendage is 6 mm. long. The proximal stele itself is poorly preserved and the plates indistinguishable.
. Bulletins of American paleontology. Australian carpoids: Gill and Caster 53 considerably shallower than in V. ici/k/z/s/, , and the carapace may be much less hooded over this area than in the Heathcote material. Charac- teristic undulatory prosopon lines are present on the posterior half of the plastron. The specimen is notable for the presence of both brachial spines, affixed (ball and socket articulation) at the distal lateral extremities of the theca. The better preserved exothecal appendage is 6 mm. long. The proximal stele itself is poorly preserved and the plates indistinguishable. Its area is proportionally less than in typical V. wilkinsi. The curious central plate or boss seems to be represented. Nature of styloid not shown. Considering the generally conservate organization of mitrate plastrons, such deviations as here exist in proportions from typical V. unlkins'i suggest that a considerable deviation in carapace organization may well occur in this Melbourne form. Of course variation range in V. wilkinsi is unknown, hence the taxonomic import of the smaller size and plate deviations of this Lower Silurian form remain Text-fig. 12.—Plate patterns in two Australian mitrate carpoids which show affini- ties with Victoriacystis icilkinsi Gill and Caster. A. Specimen from the Lower Silurian in the City of Melbourne, Victoria. (University of Melbourne No. 2876). B. Specimen from the Lower Devonian, Middendorp Quarry, Kinglake West, Vic- toria. This is the same horizon containing Rutroclypeus junori Withers and other species of this Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Paleontological Research Institution (Ithaca, N. Y. ); Columbia University. Ithaca, N. Y. , Paleontological Research Institution [etc. ]
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