Chlamys nuwokensis MacNeil, 1957
MACNEIL, F. S. 1957. Cenozoic Megafossils of Northern Alaska. United States Geological Survey Professional Paper, 294-C [p. 104, 120, pl. 11, figs. 4-6, 12]
1957 Chlamys nuwokensis MacNeil, 1957
F. S. MacNeil, 1957, plate 11.
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«A new type of pectenid pelecypod, whose close relationships are very much in doubt, was obtained from the lower fossiliferous beds on Carter Creek.
It may be related to Chlamys sayanus (Dall) from the middle Miocene of Florida and C. virginianus (Conrad) from the middle and upper Miocene of Maryland and Virginia. The shell of the Carter Creek species is thin and translucent like that of the C. virginianus. It is possible that the Carter Creek species is a northern representative of the C. sayanus group, possibly derived from it. On the other hand, the Carter Creek Chlamys may be related to and possibly ancestral to Fortipecten of the Pliocene and Pleistocene (?) of the Bering Sea region and Japan. The Japanese species of Fortipecten, F. takahushii (Yokoyama) has a very heavy shell but two other species (which may actually be one species), F. hallae (Dall) from a buried beach at Nome, Alaska, and F. piltunensis (Khomenko) (1931, p. 53, pl. 1, figs. 6-8; pl. 2, figs. 1-6) from the Supranutovo series (upper Pliocene or Pleistocene) of northern Sakhalin are thinner, although still moderately heavy. The Carter Creek species is more like the Atlantic Ohlaws sayanw group in having concave dorsal margins and ribs of subequal size on the two valves. Fortipecten has convex dorsal margins and the ribs of the right valve are considerably broader than those of the left valve (see MacNeil, Mertie, and Pilsbry, 1943, pl. 12, figs. 1-2; pl. 13, fig. 1). Though the ancestral relation of the Carter Creek Chlamys to Fortipecten is as yet unproved, it is equally true that Yabe and Hatai (1940) in their paper on Fortipecten could not link it with certainty to any Miocene pectenids from the Pacific region. Localities : USGS D50 (T) , D52 (T) .» [page 104]
«Shell of medium size, suborbicular; valves very little inflated, very thin and translucent. Dorsal margins concave, the posterior margin a little more so than the anterior margin and terminating in a line more nearly horizontal. Posterior margin of posterior ears strongly sloping; anterior margin of anterior ear of left valve about vertical; anterior ear of right valve incomplete on only known specimen but apparently alate with a moderate byssal sinus. Dorsal margin along byssal sinus bearing strong denticles. No well-defined submarginal areas. Sculpture similar on both valves but ribs on right valve may be slightly broader at the crest. Nine well-formed ribs on each valve and on some individuals another incipient rib at either end or both ends. Ribs narrow and some bluntly rounded on top, separated by broad evenly concave interspaces that rise gently to the crest of the ribs. Secondary radial lirations in the interspaces, and in individuals whose ribs are not flattened on top they may be present on top of the ribs as well; 8 to 14 secondary radial lirations in each interspace. The alate anterior ear of the right valve with 3 to 4 strong radials; all other ears sculptured with fine lirations similar to the secondary lirations on the disc but sometimes made beaded by growth lines. Raised slightly irregular concentric lamellae extend across the crest of the ribs and on the secondary radial lirations form tiny upright crescentic spines, but there is no suggestion of a metal lathlike sculpture of the type found in the C. isladicus group. The ligament pit is shallow and inclined slightly to the posterior.
Holotype: A left valve (fig. 4), USNM 561866. Paratypes: left valve (fig. 5), USNM 561867, left valve (fig. 6) USNM 561868, right valve (fig. 12), USNM 561869. Dimensions of holotype: length, 60 millimeters. The relationships of this species are by no means clear. The concave dorsal margins, scabrous surface and rib pattern recall C. sayanus Dall from the Miocene of Florida (see Tucker-Rowland, 1938, pl. 2, fig. 6). Another possibly related species which has primary ribs only near the beaks, but which has a thin translucent shell like C. nuwokensis occurs in the Miocene of Virginia; C. virginianus (Conrad) (see Tucker-Rowland, 1938, pl. 5, fig. 14). The ribbing of C. nuwokensis at least superficially resembles that of the left valve of Portipecten hallae (Dall) from the Pliocene or Pleistocene of Nome, Alaska (see MacNeil, Mertie, and Pilsbry, 1943, pl. 12, fig. 1), but the latter is a moderately heavy shell and the sculpture of the right valve is quite different. Moreover, F. hallae has a metal lathlike microsculpture. Fortipecten also occurs in the Pliocene of Japan (see Yabe and Hatai, 1940). Pecten kagamianus Yokoyama, 1929, pl. 1, fig. 1) is a possible relative of both C. nuwokemis and P. hallae but, if so, it is impossible at this time to say how closely and through what intermediate species they are related. Horizon: Miocene (?) . Type locality: Carter Creek, a stream flowing into Camden Bay, Alaska. About latitude 69°57'45" N., longitude 144°46' W. From a section 210 to 258 feet below the top of a measured section. Collector, Robert H. Morris, 1953. Locality, USGS D50 (T).» [Page 120]
FRANCIS STEARNS MACNEIL, 1957
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