Chlamys islandica kanagae MacNeil, 1967
MACNEIL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. United States Geological Survey Professional Paper, 553: iv, 57 p., pls. 1-25. [p. 35, pl. 13, fig. 6; pl. 15, fig. 3 ; pl. 17, figs. 1-8; pl. 18, fig. 1]
1967 Chlamys (Chlamys) islandica kanagae MacNeil, 1967
F. S. MacNeil, 1967, plate 13.
F. S. MacNeil, 1967, plate 15.
F. S. MacNeil, 1967, plate 17.
F. S. MacNeil, 1967, plate 18.
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«Pecten n. sp. B. aff. P. albidus, MacNeil in Fraser and Barnett, 1959, U.S. Geol. Survey Bull. 1028-I, p. 218.
Description.— Shell of medium size, subrounded, medium inflated. Ears similar or slightly shorter than in typical C. islandica. Sculpture of right valve ranging from uniformly nonplicate or nonfasciculate to moderately fasciculate; fascicles are flat topped and bear from three to six riblets; interspaces are concave and shallow, about the same width as the fascicles, and contain from three to six riblets. Left valve ranges from moderately strongly fasciculate to weakly fasciculate; some fascicles or plicae are rounded and solid, dividing weakly near the margin; some fascicles are moderately high and divided into three to four riblets throughout most of their length; other fascicles are narrow and low, with a single riblet along the crest; interspaces are moderately broad and may contain from four to nine riblets that may be of subequal size or divided into secondary and tertiary series. Eiblets of both valves are finely beaded or scabrous, the closely set scales adding considerably to the apparent thickness. Microsculpture of adults nonreticulate and where seen consists of very fine straight radial lines. Some juvenile left valves have reticulate or metal lathelike microsculpture over the riblets and interspaces alike; this microsculpture terminates abruptly in the late juvenile stage and is followed by radial microsculpture. Discussion.— Some of the variants of this subspecies approach C. pseudislandica plafkeri. Right valves have similar flat-topped fascicles, and many left valves have moderately large smooth primary ribs or plications. The riblets of C. i. kanagae are finer and more scabrous, however, and the primary interspaces or interplicae of the left valve have more riblets. One specimen (pl. 13, fig. 6) from the upper part of the Middleton Island section is tentatively identified as C. i. kanagae. C. islandica powersi from Pleistocene beds on Amchitka is undoubtedly the closest known relative of C. i. kanagae. The shell of C. i. powersi tends to be more inflated and twisted, and the riblets are finer, more widely spaced, and less scabrous. The two living Pacific subspecies of C. islandica, C. i. albida (Dall) (see Arnold, 1906, pl. 52, figs. 2, 2a) from Unalaska and C. i. erythrocomata (Dall) (pl. 21, figs. 8, 9) from the Okhotsk Sea probably are descended directly from the C. i. kanagae-powersi stock. All these forms have similar microsculpture, reticulate in juveniles and finely radial in adults. Of all the known Pleistocene pectinids in the Pacific, C. i. kanagae is the most likely ancestor of typical C. islandica. The typical form of C. islandica has no fascicles and the riblets are subequal in size. C. i. thulensis (pl. 18, fig. 2), here described from late Pleistocene or postglacial beds of Greenland, has weak fascicles, however, and it is intermediate both morphologicaly and geographically between C. i. kanagae and C. islandica islandica. Types: The holotype (USNM 645011), a right valve, measures 73 mm in height and 67.5 mm in length. The paratype (USNM 645012) is a left valve. Other figured specimens are numbered USNM 645013-645021. Type locality: Green tuffaceous sandstone along west side of the northeastern peninsula of Kanaga Island, north of coastal lakes and about 4.5 miles south southwest of Kanaga Volcano, ceneral Aleutian Islands, USGS D3. Other occurrences: Unnamed Pleistocene formation on Adak Island, central Aleutian Islands, USGS 16907; upper part of section (early Pleistocene) on Middleton Island, Alaska, USGS M1742.» FRANCIS STEARNS MACNEIL, 1967
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