Turek, Vojtach 1978 04 15: Biological and stratigraphical significance of the Silurian nautiloid Circular or elliptical structures described as the genus Aptychopsis Barrande 1872 (and mostly referred to the Crustacea) represent the opercula of a specialized group of orthoceratids. Their morphology bears a considerable resemblance to the structure of the lower jaws (aptychi) of some Mesozoic ammonoids, particularly of the genus Physodoceras. Because of its size and structure, however, Aptychopsis cannot have functioned as a jaw apparatus. Observation of an operculumin siru supports this assumption as regards its functional and systematic position. The classification of the genus Aptychopsis as given by Jones and Woodward (1872–1893) is purely typological and hardly applicable in palaeobiology. Continuous gradations exist between the various morphological types. The lack of systematically distinctive features explains the unsuitability of Aptychopsis for biostratigraphical use. Aptychopsids occur in the Silurian of Central Bohemia between the Spirograprus turriculatus Zone and the Neodiversograptus nilssoni Zone, inclusive, with maximum frequency in the uppermost Wenlockian.

No abstract

Superfamily Rutoceratoidea Hyatt, 1884 (Pragian to Frasnian, Devonian) includes nautiloid cephalopods having exogastric cyrtoceracone or coiled shells with periodic walls or raised growth lines (megastriae) forming ridges, sometimes modified in various ways into collars, frills, or different outgrowths. High disparity and intraspecific variability of the shell form and sculpture of the rutoceratoids are conspicuous among Early Palaeozoic nautiloids. Consequently, rutoceratoids are divided according to different patterns of growth structures into three families. Parauloceratidae fam. nov. (Pragian to Emsian) contains taxa with cyrtoceracone shells and simple recurrent ribs with ventral sinus. Family Hercoceratidae Hyatt, 1884 (Pragian to Givetian) comprises forms with periodically raised ridges with three lobes forming ventrolateral outgrowths during shell growth such as wings, nodes or spines. Family Rutoceratidae Hyatt, 1884 (Pragian to Frasnian) encompases taxa having growth ridges with ventral lobe transforming into undulated frills or distinct periodic collars (megastriae). All of these families had already appeared during early radiation of rutoceratoids in the Pragian. The early radiation of rutoceratoids is, however, adequately recorded only from the Prague Basin. Rutoceratoids become widespread within faunas of Old World and Eastern American realms later during the Emsian and especially Middle Devonian. Three new genera are erected: <i>Parauloceras </i>gen. nov., <i>Otomaroceras </i>gen. nov. and <i>Pseudorutoceras</i> gen. nov. The Pragian <i>Gyroceras annulatum</i> Barrande, 1865 is assigned to the genus <i>Aphyctoceras</i> Zhuravleva, 1974. Rutoceratoids are thus represented by six genera and eight species in the Pragian Stage of the Prague Basin. In addition, variability of shell coiling among rutoceratoids and its significance for their systematics are discussed

The Devonian nautiloids Hercoceras Barrande, 1865 and Ptenoceras Hyatt, 1894 are closely related and should be classified within the single oncocerid family of Hercoceratidae Hyatt, 1884, which has priority before the family Ptenoceratidae Teichert, 1939. This is supported particularly by the similarity of their embryonic shell and by the character and ontogeny of ventrolateral outgrowths. The intraspecific variability of shells in Hercoceras mirum Barrande, 1865 (Lower Devonian, Prague Basin, Czech Republic) is striking and unusual among nautiloids. The variability in Ptenoceras alatum (Barrande, 1865) is also high, demonstrating fluent transitions between individual morphotypes. Therefore, the other two species of this genus described from the Pragian Stage of the Prague Basin, Ptenoceras modicum (Barrande, 1877) and Ptenoceras barrandei Zhuravleva, 1974 should be assigned to the single species Ptenoceras alatum

Five cephalopod specimens from the Lower Devonian of Bohemia (Czech Republic)