The North Pacific Miocene record of Mytilus (Plicatomytilus), a new subgenus of Bivalvia

Abstract

I Washington, and the early middle Miocene Kuluven suite of western A new subgenus of large plicate fossil mussels of the North Pacific, Mytilus (Plicatomytilus) n. subgen., includes three distinct species, Mytilus (P.) middendorffi Grewingk, 1850, Mytilus (P.) gratacapi n. sp., and Mytilus (P.) n. sp. This extinct subgenus ranged from central California to western Kamchatka during the Miocene. Plicatomytilus is distinguished by strong plications of the shell which deflect the plane of commissure and by the foot retractor muscle scar which is separated from the posterior byssal retractor and-Kamchatka, U.S.S.R. This previously unrecognized taxon is not, however, referable to Plic~tomytilus. Mytilus middendorffi occurs in provincial middle Miocene deposits of (1) the Narrow Cape Formation, Kodiak Island, Alaska, (2) the upper part of the Astoria Formation, Tillamook County, Oreg., (3) an unnamed formation at Coos Bay, Oreg., (4) the lower (Miocene) part of Diller's (1903) Empire Formation near Cape Blanco, Oreg., (5) the

Molluscan paleontology of the lower Miocene Clallam Formation, northwestern Washington

“…The secondary ridge distinguishes the Clallam species from M. tichanovitchi. As noted by Allison and Addicott (1976), this Mytilus n. sp. also occurs in strata of provincial early Miocene age in central California and in strata of early middle Miocene age (Gladenkov, 1974) Previously undescribed elongate, strongly inflated specimens of Solamen similar to the Oligocene species S. porterensis (Weaver, 1912, pl.…”

“…This relation is implicit in the foraminiferal correlations between the Clallam Formation and California Coast Range sections based on benthonic assemblages (Kleinpell, 1938;Rau, 1964). Still, most, if not all, of the previous age assignments of the Clallam by moll usc an specialists (Etherington, 1931;Durham, 1944;Moore, 1963;Addicott, 1967Addicott, , 1969Addicott, , 1970b (Allison and Addicott, 1976). This rugose species has sometimes been confused with the middle Miocene index M. middendorffi (Allison and Addicott, 1976), a species that may be its progeny.…”

“…Still, most, if not all, of the previous age assignments of the Clallam by moll usc an specialists (Etherington, 1931;Durham, 1944;Moore, 1963;Addicott, 1967Addicott, , 1969Addicott, , 1970b (Allison and Addicott, 1976). This rugose species has sometimes been confused with the middle Miocene index M. middendorffi (Allison and Addicott, 1976), a species that may be its progeny. The more commonly occurring and more widespread pectinid, V ertipecten fucanus, provides the strongest evidence of an early Miocene age in terms of the mega-invertebrate sequence.…”

Geologic studies of the lower Cook Inlet COST No. 1 well, Alaska outer continental shelf

“…The Narrow Cape Formation here is disconformable with the Sitkinak Formation. The exposures at both places contain abundant fossils; however, at Narrow Cape the fossils indicate an early and middle Miocene age, and at Sitkinak Island, they indicate a late Oligocene or early Miocene age (Allison and Addicott, 1976). The strata represent marine shelf deposits.…”

Shorter contributions to paleontology and stratigraphy

“…aff. M. tichanm·itchi Makiyama of Allison and Addicott ( 1976), and Macoma optira (Yokoyama). and the gastropods Prisn~fltsus aff.…”