Chlamys breidavikensis 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. 16, pl. 25, figs. 4-8]
1967 Chlamys ("Chlamys") breidavikensis MacNeil, 1967
F. S. MacNeil, 1967, plate 25.
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«Description. — Shell moderately large, subrounded, left valve more inflated than right valve. Anterior ear of right valve moderately short and broad, byssal notch moderately shallow and V-shaped; posterior ear moderately short, posterior margin nearly straight and sloping at about 45°. Anterior ear of left valve moderately short and broad, anterior margin nearly vertical; posterior ear short and steeply sloping. Dorsal margins subequal or anterior margin slightly straighter and more elongate. Dorsal slopes of left valve broader and more undercut than on right valve. Kibs moderately fine with only 1 or 2 ribs showing any tendency to divide; right valve has about 90 ribs, 8 to 10 of which are on the dorsal slopes; a few of the terminal ribs might be regarded as interstitial riblets, but they are nearly as strong as the other ribs. Anterior ear of left valve has about 15 fine ribs. Ribs low, sculptured only by growth lines. Interspaces shallow and bearing reticulate microsculpture on the right valve; left valve interspaces may have reticulate microsculpture on early stages but in later stages they are smooth or have raised concentric lamellae.
Discussion.— C. ("C.") breidavikensis has about 30 more ribs than C. islandica on half-grown individuals. Large individuals of C. islandica may have about 90 riblets near the ventral margin, but many of the ribs divide once or twice to produce that number; very few of the ribs of C. breidavikensis bifurcate. Both of the posterior ears of C. islandica have a more sinuous margin and fewer and coarser ribs. Both C. breidavikensis and C. tjornesensis have been reported in previous lists as C. islandica, but neither is that species, nor am I convinced that either is very closely related to C. islandica. In my opinion, C. breidavikensis is more closely related to the group of C. multistriata and C. tauroperstriata; typical C. islandica is more closely related to early Pleistocene forms in the northern Pacific. If an until intermediates are found, however, that definitely link C. breidavikensis with some other species, the exact relationships of all these species will remain in doubt. Types: The holotype (USNM 644897), an incomplete right valve, has a length of 72 mm. The paratype (USNM 644898) is an incomplete left valve. Other figured specimens are numbered USNM 644899-901. Type locality: Base of the highest fossiliferous bed in the Breidhavik section, beach southwest of lighthouse at Valadalstorfa, Tjörnes, northern Iceland (horizon probably early glacial Pleistocene), USGS M2153.» FRANCIS STEARNS MACNEIL, 1967
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