Browsing by Author "Yochelson, Ellis Leon, 1928-"
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Item Permian Gastropoda of the southwestern United States. 1. Euomphalacea, Trochonematacea, Pseudophoracea, Anomphalacea, Craspedostomatacea, and Platyceratacea. Bulletin of the AMNH ; v. 110, article 3(New York : [American Museum of Natural History], 1956) Yochelson, Ellis Leon, 1928-; Bowsher, Arthur Leroy, 1917-"The present paper contributes to the systematic summation of the Permian gastropods of the United States by describing members of six superfamilies from this largely unknown assemblage. The finest Permian section in the United States is in western Texas. Many of the limestones there yield quantities of silicified fossils upon solution in hydrochloric acid. Collecting and acidizing programs of the United States National Museum and the American Museum of Natural History have resulted in the accumulation of large gastropod collections, which form the basis for this work. In addition, smaller collections of both silicified and non-silicified specimens from other areas have been treated. Following a brief review of the technical terms and methods employed in description, some comments on the paleoecology are given. Gastropods occur chiefly in four kinds of assemblages. A characteristic example of each of these assemblages is described, and from the evidence presented it is concluded that two of these four are transported and mixed and two are approximately in situ. It is concluded that most gastropods were from shallow water, where algae were most abundant. Attention is called to possible differences between 'limestone' and 'shale' gastropod faunas, but collections available do not permit one to draw any conclusions at this time. The main part of the paper is given to systematic descriptions of species, genera, and higher categories. All diagnoses and descriptions are original. Superfamilies diagnosed are the following: Euomphalacea, Trochonematacea, Pseudophoracea, Anomphalacea, Craspedostomatacea, and Platyceratacea. Families diagnosed are the following: Euomphalidae, Omphalotrochidae, Trochonematidae, Pseudphoridae, Anomphalidae, Craspedostomatidae, and Platyceratidae. The Craspedostomatidae are divided into three subfamilies: Craspedostomatinae, Brochidinae, and Dichostasinae. The last two are new categories. Genera or subgenera heretofore known and rediagnosed are Straparollus (Euomphalus), Amphiscapha (Amphiscapha), Omphalotrochus, Cyclites, Anomphalus, Brochidium, and Platyceras (Orthonychia). Brochidium has not previously been reported in the Permian of North America. New genera or subgenera recognized are Amphiscapha (Cylicioscapha), Straparollus (Leptomphalus), Planotectus, Babylonites, Discotropis, Diploconula, Sallya, and Dichostasia. The remainder of the paper consists of descriptions of species of the genera listed above. These include two Pennsylvanian species, deemed pertinent to the Permian studies and not described or illustrated since the original diagnosis, and 45 Permian species given in approximate stratigraphic order. Thirty-nine of the Permian species are considered to be new, and 30 species are well enough known to warrant being formally named. Variation in one species of Platyceras (Orthonychia) is considered to be caused by the specimens' being modified to conform to the calyx of several different crinoids. Occurrence data given in connection with all the Permian species are summarized on a single table"--P. 179.Item Permian Gastropoda of the southwestern United States. 3. Bellerophontacea and Patellacea. Bulletin of the AMNH ; v. 119, article 4(New York : [American Museum of Natural History], 1960) Yochelson, Ellis Leon, 1928-"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.