Lituyapecten falorensis (MacNeil, 1961)
MACNEIL, F. S. 1961. Lituyapecten (new subgenus of Patinopecten) from Alaska and California and Stratigraphic occurrence of Lituyapecten in Alaska. United States Geological Survey Professional Paper, 354-J: 225-239, pls. 35-46 [p. 234, pl. 38, figs. 1, 3; pl. 44, figs. 2, 4; pl. 45, figs. 2, 4; pl. 46, figs. 1-4]
1961 Patinopecten (Lituyapecten) falorensis MacNeil, 1961
F. S. MacNeil, 1961, plate 38.
F. S. MacNeil, 1961, plate 44.
F. S. MacNeil, 1961, plate 45.
F. S. MacNeil, 1961, plate 46.
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«Shell moderately large; suborbicular to weakly extended posteriorly; valves moderately inflated; right valve slightly more inflated than left valve; shell moderately thin. Posterior dorsal margin moderately concave, and anterior margin nearly straight; left valve with low but sharp steplike submarginal slopes, and right valve slopes less sharp because of inflation of ears. Dorsal margin of ears straight. Ears sculptured by radial riblets with moderately strong beads, about seven riblets on posterior ear of left valve; posterior ears longer and with stronger radial riblets than anterior ears; no denticles along byssal sinus; dorsal margin of left ear of left valve with a weak swelling or fold. Ribs 21 to 23. Right valve often having a split rib, one segment having no counterpart on left valve; right valve ribs broad with undercut sides, interspaces narrow and deep; bottoms flattened; central ribs flattened or rounded on top; terminal ribs with a median sulcus which at the margin may be nearly as deep and wide as the primary interspaces. Left valve ribs moderately broad with a row of short flanges or denticles along each side; central area depressed and troughlike; three terminal ribs on each side narrow and with a single row of short flanges on their crest; interspaces round-bottomed and narrower than the ribs on some specimens, wider on others; no interstitial riblets on any specimens observed. Juvenile microsculpture unknown.
Holotype, both valves together (right valve, UC 34172, left valve UC 34171) measures; diameter 107 mm, height 99 mm. Figured specimen UC 15977 has a height of 130 mm. The specimen figured by Manning and Ogle, refigured here and made the holotype of the species, is the only specimen of a yakatagensis-like Lituyapecten figured previously other than the type of yakatagensis itself. Its relationship to yakatagensis was not recognized and instead, it was identified tentatively as a variety of P. oregonensis Howe, a species described from the Empire formation of western Oregon. Possibly the association of this species with oregonensis came about because of the incorrect locality data given by Howe for a specimen he figured. This specimen (Howe 1922, pl. 11, fig. 2) was stated by Howe to be from the Wildcat series of Humboldt County, Calif.; but according to its number (N. P. 82 of the Arnold catalog; not 28 as stated by Howe), it comes from north of the mouth of the Raft River, Taholah, Grays Harbor County, Wash., a locality of indefinite formational assignment. There might have been some question, had the specimen figured by Howe actually come from the Wildcat series, as to whether it was oregonensis or falorensis, because it is very difficult to identify right valves, even on specimens whose left valves are very dissimilar. However, its correct locality together with the fact that it compares favorably with other right valves of oregonensis makes it safe to assume that it belongs to that species. There are two specimens in the Manning and Ogle collection besides the holotype. They are smaller than the type, but they appear to have narrower ribs than the corresponding stage on the type. In this respect they approach some of the typical specimens of P. purisimaensis. The left valves of these two specimens have narrow but definitely flat-topped ribs with denticulate margins like the specimen from the Purisima formation illustrated on plate 45, figure 2, here referred to P. (L.) falorensis. Typical P. (L.) purisimaensis, on the other hand, has narrow rounded ribs over most of its disk with two or three of the central ribs slightly wider and having a weak concavity along the crest. (See pl. 44, figs. 1, 3.) The Purisima formation also contains a form that has wide ribs on the right valve and broad, flat-topped ribs with marginal denticles on the left valve (pl. 44, figs 2, 4), and that compares favorably with the type of falorensis. Although it is difficult to say how many species are involved here and, if they are distinct, just what the varietal range of each species is, it is fairly certain that purisimaensis and falorensis are very closely related. P. (L.) yakatagensis is a highly variable species if all the specimens here referred to it are really conspecific. The same range of variation has not been noted in lituyaensis, but possibly all variants of that species have not been found. If approximately the same range of variation could be demonstrated for lituyaensis, a strong case for considering falorensis as a variety or, at most, a subspecies of purisimaensis could be made. To state the problem another way, it is not known whether purisimaensis and falorensis represent divergent stocks of common but not too distant ancestry or whether the three species, yakatagensis, lituyaensis, and purisimaensis (including falorensis) are linear elements of one very variable stock, no parts of it having been clearly set off by geographical isolation. If the latter were so, all the variants existing at any particular instant of time belonged to one species, whereas the mean of variation shifted sufficiently through time to make at least three distinct species recognizable. The Stanford University collection contains another specimen from the Purisima formation (pl. 45, fig. 4; pl. 46, fig. 1) that has wide ribs on the left valve like those of typical falorensis. However, the right valve has high, comparatively narrow ribs that approach those of typical purisimaensis. Furthermore, some of the intapaces on the right valve have strong interstitial ribs, almost as strong as those of P. (L.) poulcreekensis. On the basis of its left valve, and because some individuals of falorensis have narrower ribs than the type, I am identifying this specimen as falorensis. A similar specimen, except that it lacks interstitial ribs, is in the University of California collection (UC 32659). Distribution.— Pliocene, northern and central California: Falor formation of Manning and Ogle, 1950, northern Humboldt County; Rio Dell formation of Ogle, 1953 (Wildcat series of Lawson, 1894), Humboldt County; Purisima formation, San Mateo County, Calif. Type locality.— Falor formation, near bridge crossing Boulder Creek, adjacent to the Wiggins Rach, about 10 miles southeast of Blue Lake, Humboldt County, Calif., UC A4233. Other occurrences.— Falor formation, SU 4837; Rio Dell formation, SU 4932, SU 4937; Purisima formation, UC 1780 (32659), UC 1788, UC A4343, SU 1095, SU 29788.» FRANCIS STEARNS MACNEIL, 1961
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