Euvola sol (Brown & Pilsbry, 1913)
BROWN, A. P. & H. A. PILSBRY. 1913. Fauna of the Gatun Formation, Isthmus of Panama. Part 2. Proceedings of the Academy of Natural Sciences of Philadelphia, 64: 509-519 [p. 513, pl. 23 (not 24), figs. 1, 2]
1913 Pecten (Amusium) sol Brown & Pilsbry, 1913
A. P. Brown & H. A. Pilsbry, 1913, plate 23.
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«The shell is subcircular, thin, but slightly convex, nearly smooth (the growth-lines being very faint) except near the beaks, where there are radial riblets, low, rounded, but very distinct for a distance of about 10-14 mm., then gradually becoming weak and disappearing. In the left valve the beak is depressed, almost flat, and the auricles are marked off by a small ledge, but no decided change in the general curvature of the surface. In the right valve the beak is somewhat convex and separated from the more distinctly demarked auricles by a groove. Internally the shell has radial ribs in pairs, the interval between the ribs of a pair being about onethird the width of the interval between pairs.
Two valves, cotypes, measure 83 mm. from beaks to basal margin. Some specimens represented by internal casts are larger, up to 90 mm. in altitude in the case of a large one. This valve measured 90 mm. in length. From a bed with Pecten oxygonum optimum in the Culebra Cut, near Tower N, Las Cascades. This species and Pecten oxygonum optimum are characteristic fossils of what we have called the Pecten bed, at Tower N. This Amusium differs from Pecten toulae, of the Gatun bed, P. papyracea Gabb, of Santo Domingo, and the North American P. mortoni by having strong radial sculpture in the early neanic stage: those species agreeing with the recent Oriental forms in having no external radial sculpture at any stage. P. lyonii Gabb, described from Sapote, Costa Rica, agrees with P. sol in having radial beak sculpture, but it differs by having more distinctly defined auricles and by the internal sculpture of numerous equidistant ribs. While the ribs of one valve are not perceptibly twinned in the Oriental Amusiums, they are about equal in number in the two valves in P. pleuronectes L., in which this character of having one valve with equally spaced ribs and one with paired ribs is very pronounced. With the single exception noted below, all of the casts we have seen from the Pecten bed agree in having ribs in contiguous pairs. In one incomplete cast the ribs are in pairs separated by intervals fully half as wide as the spaces between pairs (not crowded as in P. lyonii Gabb). This probably represents another species.» AMOS PEASLEE BROWN & HENRY AUGUSTUS PILSBRY, 1913
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«Of medium size, height little less than length. Right valve slightly convex, left valve very slightly convex. Auricles not ribbed; right auricles slightly more depressed than left; byssal notch shallow. On both valves, riblets extending from tip of umbo for distance of 9 to 12 mm. Interior lirae extending far up from ventral margin. On right valve lirae paired, 13 to 15 pairs. On left valve, lirae generally paired, 12 or 13 pairs, exceptionally equidistant. Lirae showing through to exterior on some valves. A pair of
cardinal crura and a pair of elongate auricular crura, ending in a tubercle. Length (almost complete) 80.5 mm, height (almost complete) 79.5 mm, convexity about 5 mm (figured left valve). Type material: Lectotype, herewith designated, the valve illustrated in Brown and Pilsbry's figure 2, Acad. Nat. Sci. Philadelphia 3888. Type locality: "Pecten bed" at tower N [Panama Canal, west side of Las Cascadas Reach], Canal Zone, La Boca formation. All the unequivocally identified valves of Amusium sol are topotypes, or virtual topotypes. In three of the four collections, however, exteriors that lack the umbonal area and interiors are doubtfully identified. Brown and Pilsbry's specimens were collected from what they designated as the "Pecten bed" at tower N, a signal tower on the pre-Canal alinement of the Panama Railroad. During the construction period, the railroad in that part of Gaillard Cut was close to the west bank of the present canal. MacDonald (1919, p. 537-539) measured 215 feet (65.5 m) of La Boca strata, upward from the base of the formation in the tower N area. He found A. sol in his units 16 and 19 near the top of the section (localities 99f and 99g, respectively). Unit 19 presumably is the "Pecten bed." The specimens from localities 119 and 119a also are from that unit. At locality 99f, A. sol is associated with Flabellipecten antiguensis; it is not known to be associated with Amusium toulae, the next species, although interiors of the two species are indistinguishable. In America, umbonally ribbed species of Amusium are known only in the Miocene of the Caribbean region. The first described species, A. lyonii (Gabb, 1881a, p. 347, pl. 45, figs. 24, 25a, 25b) was collected by Gabb at his unrecognizable early Miocene locality, Sapote [Zapote], on Rio Reventazón in northeastern Costa Rica. Though the type material consists of fragments, the auricles are longer than those of A. sol and are more depressed. Occurrence: La Boca formation (early Miocene), Gaillard Cut area, localities 99f and g, 119, 119a. WOODRING, W. P. 1982. Geology and paleontology of Canal Zone and adjoining parts of Panama. United States Geological Survey Professional Paper, 306-F: 1-759, pls. 83-124. [p. 587]
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Amusium sol (Brown and Pilsbry); W. P. Woodring, 1982, Geology and paleontology of Canal Zone and adjoining parts of Panama, plate 98, figure 12.
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