Propeamussium interradiatum (Gabb, 1869)
GABB, W. M. 1866-1869. Paleontology of California. Vol II. Cretaceous and Tertiary fossils. Geological Survey of California, 299 p., pls. 1-36 [p.199, pl. 33, fig. 98, 98a]
1869 Pecten interradiatus Gabb, 1869
1923 Pecten (Propeamusium) [sic] vacavillensis D. B. K. Palmer, 1923
1923 Pecten (Propeamusium) [sic] vacavillensis D. B. K. Palmer, 1923
W. M. Gabb, 1866-1869, plate 33.
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«SHELL small, subcircular, equivalve, equilateral, compressed, thin; upper valve, ears equal, moderately large; lower valve, right ear long, deeply and narrowly emarginate. Surface marked by very numerous fine radiating lines, and obscure lines of growth. Internal surface of both valves bearing eight straight, equidistant, large ribs, of variable length among themselves, extending from the beaks to near the middle of the shell, and ending abruptly.
Figures, natural size.
From a buff-colored shale east of New Idria, at or very near the summit of the Tejon Group, where I found it very abundant. P. operculiformis and P. Californicus of the California Cretaceous are marked by concentric lines only; the former is much larger than the present species, and the ears are of a very different shape; neither of those species has the internal ribs of this shell. The other species are longer, with smaller ears, and are markedly costate.» WILLIAM MORE GABB, 1869
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«Lectotype.— ANSP 4652 (Stewart, 1930). [Inadvertently cited by Stewart as ANSP 4442.] Holotype of Pecten (Propeamussium) vacavillensis Palmer, UCMP 30596.
Type locality.— Of Propeamussium, interradiatum: East of New Idria [Priest Valley quad., San Benito County], Calif. Kreyenhagen Shale, Eocene and Oligocene; of Pecten (Propeamussium) vacavillensis: UC 3573, Solano County, Calif. Capay Formation, Eocene. Supplementary description.— Addicott (1971, p. 229) notes that whereas the ears and the length of the internal ribs on one of the original hand-drawn illustrations representing a left valve of P. interradiatum (Gabb, 1869, pl. 33, fig. 98) indicate reference to Propeamussium (Propeamussium), the other illustration of a portion of the dorsal margin of a right valve (figure 98a) indicates a deep byssal notch and an extremely narrow right anterior ear, suggesting that the figures are of entirely different taxa. Comparison.— Propeamussium interradiatum (Gabb) differs from P. leohertleini Addicott (1971), described from the Eocene of Alaska, in having a relatively smooth exterior and fewer internal ribs —8 rather than 10. (Addicott, 1971, p. 227) "It seems doubtful that Propeamussium stanfordensis [Arnold, 1906] represents young specimens of the well-known Eocene species P. interradiatum (Gabb) as was suggested by Grant and Gale (1931). The shorter, consistently fewer internal ribs —8 rather than 10 or more— and the weaker, much finer concentric sculpture of P. interradiatum * * * permit differentiation." (Addicott, 7971, p. 229) Comments.— The lectotype of P. interradiatum, presumably a left valve, does not have the external shell preserved. It bears eight internal ribs; three posterior ribs are straight, the remaining five curve toward the anterior margin. The holotype of Pecten (Propeamussium) vacavillensis is a juvenile specimen (1.4 mm high and 1.4 mm wide), broken subsequent to its original illustration, that was distinguished from P. interradiatum by Palmer (1923, p. 301) as follows: " P. vacaviIlensis differs from P. interradiatus Gabb in that the internal ribbing occupies only the ventral two-thirds of the shell instead of the dorsal half as indicated in the original figure." As noted by Stewart (1930, p. 124), on small specimens of P. interradiatum the internal ribs reach almost to the ventral shell margin. Geographic range.— Middle California. Geologic range.— Eocene. Occurrence in California.— Eocene: Butano (?) Sandstone (Addicott, 1971), Capay Formation (Palmer, 1923), lower part of Kreyenhagen Shale (Addicott, 1971), and Tejon Formation (Arnold, 1906).» MOORE, E. J. 1984. Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae. United States Geological Survey Professional Paper, 1228-B: iv + B1-B112, figs. 1-2, pls. 1-42. [p. B7]
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Propeamussium interradiatum (Gabb); E. J. Moore, 1984, Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae, plate 1, figure 1.
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