Parvamussium leohertleini (Addicott, 1971)
ADDICOTT, W. O. 1971. Some Paleogene mud pectens of the genus Propeamussium from Alaska and California. The Veliger, 13 (3): 226-230, figs. 1-13. [p. 227, figs. 1, 2, 7, 9, 12, 13]
1971 Propeamussium (Propeamussium) leohertleini Addicott, 1971
W. O. Addicott, 1971, figures 1-13.
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«1969. Propeamussium cf. P. stanfordensis (ARNOLD). SCHOOL, GREENE, ADDICOTT, and others, Amer. Assoc. Petroleum Geologists Bull. 53: 459
«Description: Small, thin-shelled with equal auricles. Valves circular, equidimensional with similar external sculpture. Surface of right valve almost smooth; extremely fine pattern of faint concentric undulations discernible on some specimens. Right anterior auricle with weak byssal notch reflected by curvature of growth lines. Interior with 10 slightly curved ribs extending nearly ¾ of distance toward the margin. Left valve with almost equally faint but more strongly delineated sculpture of regular concentric growth lines. Interior with 10 ribs slightly curved extending nearly ¾ of distance from beak
to margin. Type: U. S. National Museum 646444, a right valve.
Dimensions of holotype: height 10.7 mm, length 10.4 mm
Type Locality: USGS Cenozoic locality M3892. About ¼ mile northwest of Mitchell Field air strip on point projecting into east shore of Lake Andrews, northern part of Adak Island, Aleutian Islands, Alaska. Andrew Lake Formation of SCHOLL et al. (1970), middle or late Eocene.
Discussion: Propeamussium leohertleini occurs in the lower part of the Andrew Lake Formation at localities about 200 m (M3891) and 350 m (M3892) above the base. It is associated with a small assemblage of benthonic foraminifers considered by R. L. PIERCE (in SCHOLL et al., 1970) to be provincially of late Eocene age [Narizian Stage of MALLORY (1959)].
Seven of the 16 specimens from the type locality have 10 internal ribs; the remainder from this locality and from nearby M3891 are incompletely preserved. Many of the latter are crushed, articulated valves on which the internal ribs are intermcshed and, in some cases, deformed ( Figure 1 ) . The delicate surface sculpture of concentric growth lines and undulations is discernible on only a few of the specimens; it appears to be crisper on the left valves. Clear-cut radial sculpture was not detected on any of the specimens. As previously indicated (SCHOLL et al., 1969) this species is very similar to Propeamussium stanfordensis (ARNOLD), a late Eocene species from central California (Figures 3, 5, 8, 10) . It differs from that species, and from the similar early Eocene species P. mideocenicum VOKES, 1939 from California, principally in lacking a well-defined byssal notch. The left valve of P. mideocenicum can be differentiated from this species by its prominent, sharp external ribs (12 on two of the syntypes: UCMP 15584 and 15586). Further, but minor, differences from the California species are the relatively shorter internal ribs and the prominent, but very fine, growth striae of P. leohertleini. Propeamussium interradiatum (GABB, 1869, p. 199; plt. 33, figs. 98, 98a), the common Eocene species of this genus from California, differs from P. leohertleini in having a relatively smooth exterior and fewer internal ribs – 8 rather than 10 (Figures 6, 11). This species is named for Leo G. Hertlein, Curator Emeritus at the California Academy of Sciences, in recognition of his contributions to the study of Tertiary and Quaternary monomyarian pelecypods. Occurrence: Andrew Lake Formation (middle or upper Eocene), Adak Island, Aleutian Islands, Alaska, USGS Cenozoic localities M3891, M3892, M4108.»
WARREN OLIVER ADDICOTT, 1971
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