Bemella, Missarzhevsky, 1969
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publication ID |
https://doi.org/ 10.4202/app.2012.0004 |
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persistent identifier |
https://treatment.plazi.org/id/03C3891D-1528-C276-FF00-F881CA76FA79 |
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treatment provided by |
Felipe |
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scientific name |
Bemella |
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Bemella View in CoL ? sp.
Fig. 4 View Fig .
Material.—Five calcium phosphatic internal moulds, including four figured specimens SMNH Mo 167650–167653 from sample 7/36.7. Emyaksin Formation, Bol’shaya Kuonamka River; correlated with the Delgadella anabara Zone, Atdabanian Stage.
Description.—Low cyrtoconic, laterally somewhat compressed shell.Apertural margin suboval in outline, narrowing towards straight subapical margin, with length/width ratio 1.8 to 2.0.Apex bulbous and somewhat compressed laterally, strongly inclined and projecting beyond the apertural margin. Sub-apical side concave and relatively short. Supra-apical side long and evenly convex. The inner surface of the shell (as reflected by internal moulds) bears concentric folds.
Remarks.—The fossils have diagnostic features of Bemella , but their assignment is hampered by incomplete preservation as smooth internal moulds.
Genus Parailsanella Zhegallo in Voronova et al., 1987
Type species: Parailsanella acris Zhegallo in Voronova et al., 1987; Fallotaspis Zone, Montezuman Stage ; Mackenzie Mountains, Northwest Territories of Canada.
Remarks.— Parailsanella includes bilaterally symmetrical, laterally compressed, slightly cyrtoconic univalves. Parailsanella is smaller in general and more laterally compressed than Ilsanella Missarzhevsky, 1981 . Ilsanella is usually represented by larger (> 1 cm) forms, with straight apertural margin, whereas in mm-sized Parailsanella (sensu Parkhaev in Gravestock et al. 2001) there is a sinus or train, which is not, however, reported from the type species, P. acris ( Voronova et al. 1987: 45, pl. 20: 1). Lateral compression is not as conspicuous as in stenothecids (see below). Parailsanella is most similar to Mackinnonia Runnegar in Bengtson et al., 1990 (see below), but the latter can be distinguished by a lower shell, strongly hooked apex and more prominent train with a pegma-like structure. Comparison with generally similar Anabaroconus Gubanov, Kouchinsky, Peel, and Bengtson, 2004 (see also Kouchinsky et al. 2011) is hampered by its different mode of preservation as silicified shells. The otherwise similar Capitoconus Skovsted, 2004 was originally distinguished from Parailsanella only by a larger and more elongated protoconch. The forms described below fit the diagnosis of Parailsanella , although without a sinus or train preserved.
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