Striatoamussium patriciae (Poulton, 1991)
POULTON, T. P. 1991. Hettangian through Aalenian (Jurassic) guide fossils and biostratigraphy, northern Yukon and adjacent Northwest Territories. Geological Survey of Canada, Bulletin, 410: 1-95, pls. 1-18. [p. 28, pl. 18, figs. 1-25]
1991 Propeamussium (Propeamussium) patriciae, 1991
T. P. Poulton, 1991, plate 18.
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«Holotype. GSC holotype 92819 from GSC locality C-81341, Kingak Formation, Johnson Creek. Upper Aalenian Erycitoides howelli Zone (PI. 18, figs. 22, 25).
Etymology. In honor of my wife.
Description and discussion. The most recent comprehensive study of the genus is by Johnson (1984) who considered all the European Jurassic specimens of Propeamussium (Propeamussium) to be resolvable into only three species--P. pumilum (Lamarck) (which he considered to include the most commonly reported Aalenian species P. personatum), P. laeviradiatum, and P. nonarium. The specimens described here from the northern Yukon area are closely similar only to the first, P. pumilum, but differ in the regularity and strength (on the juvenile shell) and wide spacing of the external ribbing. The well defined byssal notch that characterizes the only other subgenus of Propeamussium, Parvamussium, is missing on the Canadian specimens. The new species is characterized by its straight hingeline, small and nearly symmetrical auricles, absence of a byssal notch, 10 or so internal radial riblets reaching from three quarters to nine tenths (variable from one specimen to another) of the way to the ventral margin, and the regular, low-relief external radial ribbing. One specimen figured as Variamussium sp. by Efimova et al. (1968, PI. 66) is similar to P. patriciae but has more irregular; external ribs. Although the species appears to be restricted to the Aalenian in the northern Yukon area and perhaps also in British Columbia, it occurs more commonly in the Toarcian of the Canadian Arctic Islands. The closest species in Europe, P. pumilum, has a Toarcian through Lower Bajocian range according to Johnson (1984).»
TERRY P. POULTON, 1991
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«Description. Shell medium-sized to large, equilateral, sub-orbicular in outline, length slightly exceeding height. Both valves of equally low convexity, not gaping along lateral margins. Auricles of both valves well demarcated from disc, subequal in shape, the anterior one being slightly larger than the posterior. Dorsal margins of auricles straight, meeting at an angle of 180°. Right valve anterior auricle with moderately deep byssal notch; posterior margin of posterior auricle weakly concave, meeting the disc at an acute angle. Both auricles of left valve meeting disc at an acute angle. Right auricles carry a few, faint radial riblets; left auricles smooth except for growth lines.
Radial sculpture of shell exterior (Text-fig. 6A) very variable, consisting of narrow to broadly rounded ribs and riblets; number of ribs increasing to a variable degree by intercalation of new ribs during ontogeny, which may or may not gain the same strength as the original ones. Riblets separated by very irregularly spaced intervals, the latter ranging from being as wide as the riblets to up to five times the width of the riblets on the same specimen. Left valve exterior ornamentation differs from that of right valve only by presence of radial depression on posterior part of disc, which is best developed in early growth stages.
Interior of valves with a maximum of 14 (10-14) internal costae in early stages of ontogeny (e.g. Text- fig. 6B); internal costae of slightly varying strength. 10-11 of the internal costae reaching from three quarters to nine-tenth of the distance to the ventral margin in adults; others fading while approaching shell margin. Resilifer deep, triangular in shape. Remarks. P. (Striatoamussium) patriciae can easily be distinguished from all Jurassic species of Propeamussium, such as P. (Parvamussium) pumilum (e.g. JOHNSON 1984: 22, pl. 1, figs. 1-4, 7-9), P. (Parvamussium) laeviradiatum (e.g. JOHNSON 1984: 28, pl. 1, figs. 5, 6, 10, 12), P. (Parvamussium) nonarium (e.g. JOHNSON 1984: 32, pl. 1, figs. 13-14, 715-16), and P. (Parvamussium) olenekense (e.g. SEY & POLUBOTKO in DAMBORENEA et al. 1992: pl. 122, figs. 1-2; also referred to as Variamussium waageni POLUBOTKO in EFIMOVA et al. 1968: 77, pl. 41, figs. 3-6) by both valves bearing a radial sculpture.
The specimens figured as Variamussium sp. by POLUBOTKO (in EFIMOVA et al. 1968: 78, pl. 66, fig. la-b) from the Upper Aalenian of North-East Russia closely resemble P. (S.) patriciae. As the external sculpture of the Russian form is only figured from a single valve, however, its generic (and specific) status must remain open.» ABERHAN, M. 1998. Early Jurassic Bivalvia of western Canada. Part I. Subclasses Palaeotaxodonta, Pteriomorphia and Isofilibranchia. Beringeria, 21: 57-150, text-figs. 1-14, pls. 1-19. [p. 101, 102]
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Propeamussium (Striatoamussium) patriciae Poulton 1991; M. Aberhan, 1998, Early Jurassic Bivalvia of western Canada. Part I. Subclasses Palaeotaxodonta, Pteriomorphia and Isofilibranchia, plate 10, figures 17, 18; plate 11, figures 1, 3, 5, 7.
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