Permian Gastropoda of the southwestern United States. 3. Bellerophontacea and Patellacea. Bulletin of the AMNH ; v. 119, article 4

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New York : [American Museum of Natural History]
"The present study includes two superfamilies of aspidobranch gastropods from the Permian of the southwestern United States. These are the Bellerophontacea, an abundant group having primitive bilateral symmetry, and the Patellacea, a rare group showing superficial, secondary bilateral symmetry. Where possible, species described from Permian outcrops outside North America have been tentatively assigned to the genera studied. Species currently assigned to the Pennsylvanian genera of Bellerophontacea in North America have been briefly reviewed. This is the first published summary of the bellerophontacean species in 60 years. Following Knight's concept, I interpret the Bellerophontacea as being prosobranch gastropods. The slit suggests two gills, and phyletic considerations imply that these gills may have restricted them to a firm bottom in fairly clear water. The Recent Patellacea have a clinging habit, and there is strong suggestive evidence that the Permian species had a similar habit. The Permian Bellerophontacea do not show phyletic size increase through time. The size of Permian species shows no clear trends either in the fauna as a whole or in a few selected species studied in more detail. Size frequency distribution in nine samples suggests that the occasional large specimen encountered is best considered as an extremely old individual. Size frequency studies may be of some use in differentiating between biocoenoses and thanatocoenoses. Nine genera or subgenera of Bellerophontacea are described, one of which is new. Forty-five species of Bellerophontacea are discriminated. Thirty-three of these are considered new, five are redescribed, and seven are discussed but not named. The Patellacea are less varied, with two genera and seven species being recognized. Three species are new, two are redescribed, and two are unnamed. Occurrence data are presented for all species"--P. 211.
p. 209-293, [12] p. of plates : ill. ; 27 cm.
Includes bibliographical references (p. 289-293).