Parvamussium astoriana (E. J. Moore, 1963)
MOORE, E. J. 1963. Miocene Marine Mollusks from the Astoria Formation in Oregon. United States Geological Survey Professional Paper, 419: 1-109, pls. 1-32. [p. 68, pl. 21, fig. 5; pl. 22, figs. 2, 3, 5]
1963 Paramussium astoriana E. J. Moore, 1963
E. J. Moore, 1963, plates 21, 22.
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«Paramussium astoriana is a rather large (maximum size 48.1 mm long and 51.0 mm high) thin-shelled form, slightly higher than long, with small equidimensional beaks. One valve, here considered the right as defined in the generic discussion, has fine concentric lines. The other valve, here considered the left, has concentric and radial lines of equal width; the concentric lines are separated by interspaces about twice as wide as those between the radials. The shell is reinforced by 8 or 9 internal ribs of varying lengths and widths. Some of these ribs extend from the umbo across about one-half of the shell, whereas others seem to have been shorter. The ribs are usually straight from the umbonal area to their ventral end, and they are present on the central three-fifths of the shell. The ribs apparently did not curve upward at the margins. The shell seems to have been thickened along a line closely following the concentric lines and beginning with the ventral extension of the most anterior or posterior rib. A pair of well-developed and relatively strong crura are present.
Holotype: US NM 563253.
Type locality: (Loc. 10) One block south of the old high school building on Harrison Avenue, southwest corner of Ninth Street in Astoria. Figured specimens: USNM 563252, 563254, 563255. Localities: (loc. 20) Opposite 382 Alameda Avenue in Astoria; (loc. 10) Same as holotype; (loc. 19) Irving Avenue, near 37th Street in Astoria. Twenty-three specimens of this species are present in the collections. Most of these specimens are incomplete, and most are preserved as impressions in shale or limestone and lack all, or most all, of their original shell. All the specimens were collected in 1910 from the Astoria formation in Astoria, and more than half of them are presumably from the shale of Howe (1926). The following is a descriptive list of the specimens in the museum:»
ELLEN JAMES MOORE, 1963
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