Lyropecten pretiosus (Hertlein, 1925)
HERTLEIN, L. G. 1925. Pectens from the Tertiary of Lower California. Proceedings of the California Academy of Sciences [4th Series], 14 (1): 1-35, pls. 1-6. [p. 12, pl. 2, fig. 6; pl. 3, fig. 4]
1925 Pecten (Lyropecten) pretiosus Hertlein, 1925
1932 Pecten (Lyropecten) miguelensis submiguelensis Loel & Corey, 1932
1932 Pecten (Lyropecten) miguelensis submiguelensis Loel & Corey, 1932
L. G. Hertlein, 1925, plates 2, 3.
|
«Shell small. Right valve moderately arched, and ornamented by about 17 or 18 rounded, radiating ribs, separated by somewhat narrower interspaces; ribs and interspaces sculptured by fine, radiating fines and crossed by fine, concentric lines of growth; anterior and posterior margins turning down abruptly, and smooth except for incremental striae; ventral margin rounded and turned down abruptly; anterior ear with a distinct byssal notch, and a slight groove also present between ear and margin of shell; about five radiating riblets crossed by incremental lines ornament the ear; posterior ear sculptured by about six or seven radiating riblets, crossed by incremental striae, the ear sloping downward and slightly posteriorly from the hinge line. Left valve ornamented by about 14 or 15 radiating ribs, the whole surface with sculpture similar to that of right valve; ears sculptured much as on right valve. Altitude 27 mm.; longitude 29 mm.; diameter of right valve approximately 10 mm.; apical angle of right valve approximately 87°.
Type: Right valve. No. 38 (L.S.J.U. type collection), from Loc. 59 (L.S.J.U.), Turritella bed above San Gregorio Lagoon, 120 miles north of Magdalena Bay, Lower California, on the trail from Arroyo Mesquital to La Purisima ; Paratypes: No. 1770 (C.A.S. collection), from Loc. 59 (L.S.J.U.), and Nos. 89 (L.S.J.U. collection), and 1771 (C.A.S. collection), from Loc. 57 (L.S.J.U.), La Purisima Cliffs, on San RamÓn River, Lower California; E, Call Brown collector; Isidro formation, Lower Miocene. The characteristic shape, sculpture, and shape of ears distinguish this beautiful little Pecten from other species.» LEO GEORGE HERTLEIN, 1925
|
«Taxonomic comments. — A suite of specimens from the La Purisima area of Baja California Sur (UCMP B-5016), collected in 1957 by F.H. Kilmer and E.G. Allison, provided the first evidence of adult form and variability in L. pretiosus. Rib counts, ledging, growth form, and fine sculpture matched those of rare individuals formerly identified as L. submiguelensis from the northern Channel Islands. Morphologic similarity suggests conspecificity, not convergence. The closest morphologic correspondence is between specimens from loc. UCMP B-5016 and hypotypes of L. submiguelensis from Santa Rosa Island (UCMP 10136; UCSB hypotype M15, UCSB 4698 from SR 67-53). Some specimens from the La Purisima area that are identified in the literature as L. crassicardo (Beal, 1948) are L. pretiosus, others are L. sp. cf. L. magnificus.
Description. — Valves equally convex with 0-3 rounded ledges. Beaks stand slightly above the hinge line. Auricles relatively small, radially costate. Byssal notch moderately deep. Hinge line about half shell length. Umbonal angle 87°, varying with shell convexity. Right valves with 14-15 ribs (not 17-18 as originally described), weaker in anterior and posterior parts of the shell. Left valves with 14-15 ribs of which three are incipient key ribs separated by two ribs of normal strength. Rib scheme is that of the L. crassicardo-L. magnificus stock, R 2r Rc 2r R. Several individuals have slight thickenings, almost incipient nodes, where the shell forms a slight ledge. Fine macrosculpture delicate; few well-preserved left valves have been collected. The largest specimens from San Isidro (UCMP B-5012) measured 7 cm high, the largest from the Channel Islands of California 11.8 cm high (UCSB 5197 = hypotype M-18). Variability. — (PI. 26, figs. 1-9,12-14) Valves are moderately flat to convex with 0-3 rounded ledges. Juvenile interspaces with one fine riblet, adults with multiple striae. Some have 12-13 narrow, rectangular ribs, and a square right-valve anterior auricle similar to that of L. magnificus (pl. 21, figs. 1, 2). These may be variants of L. pretiosus or younger descendants of the forms common at San Isidro (UCMP B-5051, B-5016). Individuals with higher rib profiles have been collected from USGS 9157, GAS 38792, and LSJU 57; some are similar to "L." dumblei (pl. 20, fig. 9), others to L. pretiosus and L. magnificus. Precise locality and stratigraphic data are needed to evaluate their relationships. USGS 9157, collected by W.S.W. Kew in 1920, is in Arroyo San Gregorio, from outcrops along an old trail; it is probably downstream from where it was reported ("between Paso Hondo and Purisima Vieja," about 15 mi northwest of San Isidro). Specimens from GAS 38792 and LSJU 57 are found with forms like those from UCMP B-5016. Comparative notes. — Lyropecten pretiosus never attains the large size of L. miguelensis or L. crassicardo. It has finer macrosculpture and lower rib profiles than the others and tends to form slightly angular ledges in left valves. Lyropecten miguelensis has one coarse midriblet in each interspace, highly convex juvenile shells, and the right-valve umbone projecting above the hinge line. Lyropecten pretiosus has a higher rib count, 17-18, than L. miguelensis, which has 15. Phylogenetic affinities. — The left-valve rib scheme, R 2r Rc 2r R, tendency toward angular ledging and fine macrosculpture place L. pretiosus in the L. crassicardo-L. magnificus bioseries. Growth form, valve profiles, and fine sculpture differentiate L. pretiosus from L. miguelensis and L. estrellanus.» SMITH, J. T. 1991. Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province: Lyropecten, "Macrochlamis", Vertipecten, and Nodipecten species. United States Geological Survey Professional Paper, 1391: v + 1-155, figs. 1-18, pls. 1-38. [p. 64, 65]
|
Lyropecten pretiosus
(Hertlein, 1925); J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province, plate 26, figures 1-9, 12-14. |