<p>The new species †<i>Propercarina occidentalis</i> sp. nov. is described in detail and compared with other members of the genus †<i>Propercarina.</i> As far as can be stated up to now (the present materials are much better preserved than the other fossils of that genus), and apart from reaching a larger body size, it at least differs from the latter ones in the following meristics: more spines in the first (except †<i>P. problematica</i>) and second dorsal fin, and probably also a higher number of second dorsal fin rays (except †<i>P. rebeli</i>); a higher number of rayless pterygiophores between the first and the second dorsal fin; a higher number of anal fin spines (except †<i>P. pietschmanni</i>); slightly different interneural and interhaemal formulas; and, last but not least, a higher number of epurals in the endoskeleton of the caudal fin. Furthermore, there are differences in some body proportions (relative lengths of the anteriormost dorsal and anal fin spines, insertion levels of second dorsal and anal fins), and also in certain morphological details as, e.g., in the shape and location of the pre- and postzygapophyses, in the presence of a well developed neural crest on the second preural centrum (missing at least in †<i>P</i>. <i>problematica)</i>, in a partial fusion of the upper and lower hypural plates in the endoskeleton of the caudal fin (seemingly separate, except in †<i>P</i>. <i>problematica</i>), and in larger scales, especially in the smaller specimens. The systematic affiliations of the new species is extensively reconsidered, especially those to the suborder Stromateioidei within the Stromateiformes. Herein, and apart from the absence of a (toothed) pharyngeal sac that is shared with <i>Amarsipus</i>/Amarsipidae, †<i>P</i>. <i>occidentalis</i> sp. nov. shows more character states that are, e.g., matching with those of some Centrolophidae and/or Nomeidae. More precisely, and when incorporating it into a comprehensive phylogenetic analysis of the Stromateiformes, †<i>P</i>. <i>occidentalis</i> sp. nov. (possibly together with all other members of the genus †<i>Propercarina</i>) at least turns out to be a sister group of all extant members of the latter family. Moreover, some specimens are discussed that differ from the general morphological traits of the others. The majority of these deviations are probably due to well known shortcomings, that are, e.g., resulting from imperfect preservation, artifacts of preparation, and/or intraspecific variation. A few, however, may be indicative of a further speciation. Taphonomical, palaeobiological, and palaeogeographical particularities of the new records are also highlighted to some extent. The predominance of strongly curved specimens obviously resulted from the presence of prey items in their digestive tract which initiated a floating up of the carcasses and a typical sequence of decay. The absence of fish remains that are scattered over larger surface areas, in combination with the occurrence of specimens which probably completely disintegrated at the sea floor, may indicate rather restricted floating options and an interface between oxygen-free and at least hypoxic waters that locally may have existed rather close or directly above the sea floor. The presence of prey items within the gastrointestinal tract, which consist of small herrings in most of the mid-sized specimens, in combination with their absence in the smaller and larger ones, indicates an intermittent diet switch. Together with their occurrence in a formerly presumably shallow coastal bay at the margin of the Rupelian sea (as it was reconstructed for the ancient Grube Unterfeld environment), it suggests a lifestyle which completely differs from that of any extant representatives of the Stromateoidei. Their presence in the Western Paratethys also considerably expands the known palaeogeographic range of this genus, respectively family, and can be considered as a further argument for an at least temporary seaway connection to the eastern parts of the Tethys.</p>