Lyropecten terrysmithae, Powell & Ii & Millard & Garcia, 2022

Powell, Charles L., Ii, Millard, Cheryl D. & Garcia, Christine, 2020, A new Lyropecten (Pectinidae, Bivalvia, Mollusca) from the central California Miocene, USA, PaleoBios 37, pp. 1-12 : 2-7

LYROPECTEN TERRYSMITHAE N. SP.

FIGS. 1–5

Pecten (Lyropecten) estrellanus Conrad. Arnold (1906) , pl. XXI, f. 2, 2a, 2b. Not of Conrad (1857a, b). Hanna and Hertlein (1941):172, fig. 63-7. Not of Conrad (1857a, b).

Argopecten sp. Smith 1991:56, pl. 22, fig. 5, 6. Powell (2007), appendix 2.

Diagnosis — Lyropecten terrysmithae n. sp. differs from similar central California Neogene Lyropecten [ L. estrellanus ( Conrad, 1857a) and L. catalinae ( Arnold, 1906) ] in being equivalve and lacking ledges, having beaks that do not project dorsal above the hinge line, a proportionately shorter hinge line, and non-rectangular auricles. The interior of the shell shows well-defined ribs, which extend much further inward from the shell margin than those of similar-sized fossil California Lyropecten .

Holotype — CAS 5900 (articulate valves).

Paratypes —Specimen numbers: CAS 78554 (right valve), CAS 78555 (right valve), CAS 78556 (right valve), CAS 78557 (right valve), CAS 78558 (right valve), CAS 78563 (left valve).

Type localities — Holotype locality: CAS 28473. Paratype localities: CAS 78553 (spec. no. CAS 78554–78556), CAS 28473 (spec. nos. CAS 78557, 78558). See Appendix 1 for locality details.

Referred specimens and occurrences —The specimens in parentheses are bulk cataloged under the following locality numbers: CAS 28473 (19 articulate specimens; CAS 448 (four double valve specimens mostly missing their auricles); CAS 67089 (= LSJU 2607) (ten single valves); CAS 78553 (= R. Arnold field no. C1011) (seven valves); CAS 68632 (= LSJU locality 1081) (one articulate specimen, three small right valves as cf.); CAS 78561 (= LSJU specimen no. 30145) (one articulate specimen), CAS 74822 (=Schenck acquisition 146) (one articulate specimen, five small right valve, four small left valves, and three small indeterminate valves); CAS 74827 (=Schenck acquisition 1904) (one articulate specimen, one valve as cf.), CAS 74824 (=Schenck acquisition 1885) (one valve as cf. encased in sediment), CAS 68631 (= LSJU 1054, = SU 1054a) (one juvenile right valve, one valve as cf.); USGS M1969 (this collection contains poorly preserved pectinids two of which are identified to this species and three more are identified provision- ally [cf.]), USGS M3995 (three articulate specimens, and three single valves, one with a cast of the other valve, one partial single valve). See Appendix 1 for locality details.

Etymology —Named in honor of Dr. Judy Terry Smith for her contributions to our understanding of pectin biodiversity.

Description —Specimens of Lyropecten terrysmithae in the CAS collections range in height from 42.0 to 92.5 mm, and 42.6 to 95.4 mm in length ( Table 1). These specimens are medium-sized with relatively flat, un- ledged valves, of roughly uniform convexity (see Smith 1991, pl. 22, fig. 5), and are much flatter in profile than L. estrellanus (see Smith 1991, pl. 22, fig. 7). Lyropecten terrysmithae displays a length slightly greater than its height. Both valves exhibit between 16 to 20 radial ribs that are flat topped and visible on the interior of the valve from one-third to two-thirds the height of the shell. The umbos meet at the dorsal margin of the auricles with an umbonal angle between 113° to 115°.

The right valve ( Fig. 1) has flat-topped, flat-sided, strong radial ribs showing only intermittent looped growth lamellae as sculpture ( Fig. 1). The posterior disk flank has four to six radial riblets, while the anterior disk flank shows about half that number ( Fig. 1). Rib interspaces are variable and generally about half as wide as the ribs, with a wide riblet down the middle of each interspace that is channeled on both sides ( Fig. 1). The anterior auricle is vertically truncate with rounded upper and lower corners, with three to five radial costae that are narrow and rounded, a relatively shallow byssal notch, and small distinct ctenolium on well-preserved valves. The posterior auricle slants towards the posterior margin making the auricle wider at the base than at the top. The valve has a number of indistinct radial costae that

Specimen Type Height Convexity No. Status (mm) (mm)

CAS 5900 Holotype 85 93

CAS 78554 Paratype 56 60

CAS 78555 Paratype 55 60

CAS 78556 Paratype 66 67

CAS 78557 Paratype 70 71

CAS 78558 Paratype 71 72

CAS 78563 Paratype 82 86

radiate away from a point near the umbo. The minimum hinge width when compared to the overall width of the shell is approximately 47%, with a maximum of about 55%. The top of both auricles slant slightly downward towards the umbonal region. The hinge of the right valve ( Fig. 2) consists of a large resilifer, with two low, resilifer teeth adjacent, three dorsal teeth to the anterior of the broad resilifer, or and two to the posterior, expressed at different angles across the resilifer, and a large dorsal tooth on each side of the umbo, which is flat on top, with a very wide triangular base. Only a single immature left valve ( Fig. 3) from locality CAS 78553 is well enough preserved for description. This hinge consists of a triangular resilifer, with faint resilifer teeth on each side, followed by two dorsal teeth on either side, and then by a very faint linear depression just below the top of the auricles. The interior of each valve exhibits impressions of the external ribs, which extend from the shell margin one-third to two-thirds the height of the shell.

Radial ribs on the left valves are also flat-topped, and they may have an equal number or one less rib than on the right valve. On well-preserved specimens the ribs have moderately strong, looped lamellar growth lines. Well-preserved specimens also exhibit an interstitial channeled riblet that also show the looped lamellar growth lines. The anterior auricle is ornamented with up to five narrow, rounded ribs radiating outward, while the posterior auricle has numerous fine, radial costa with three to five subdued ribs which radiate at different angles than the anterior auricle. The bending downward of the ribs on the anterior auricle on the holotype is probably the result of a repaired injury, as indicated by disturbed growth lines.