Scissurella nesbittae, Geiger & Goedert, 2020

Geiger, Daniel L. & Goedert, James L., 2020, Scissurella nesbittae, new species, from the Gries Ranch Formation, Lewis County Washington State (Gastropoda: Vetigastropoda: Scissurellidae), Zootaxa 4759 (4), pp. 593-596 : 593-595

Scissurella nesbittae n. sp.

( Fig. 1 )

ZooBank LSID [According to Richard Pyle of ZooBank, Zootaxa arranges for ZooBank registrations].

Type material. Holotype SBMNH 467092 . Paratypes SBMNH 637694 (11 specimens) , UWBM 112001 – 112005, from type locality. An additional 10 specimens UWBM 112006 – 112015 .

Type locality. LACMIP locality 41621 (= UCMP loc. 3607); Gries Ranch Formation, latest Eocene or earliest Oligocene , 33–34 Ma (latest Priabonian or earliest Rupelian) ( Prothero & Burns 2001). South bank of Cowlitz River at the bend, east half of the SW ¼ of Sec. 24, T. 11 N. R. 2 W., at site of the old Gries Ranch , Lewis County, Washington. The scissurellid fossils are from silty sandstone directly below the thick oyster bed in the eastern part of the outcrop. GPS coordinates: 46.4188º N, 122.8788º W .

Etymology. Named for Elizabeth A. Nesbitt for her contributions to stratigraphy and paleontology of the Pacific Northwest.

Description. Shell to at least 1 mm (based on shell remnants on base of holotype), trochiform, suture below periphery of previous whorl. Protoconch of 0.75 whorls, fine axials, apertural varix connected to embryonic cap, apertural margin sinusoid. Teleoconch I of 1.125 whorls, about 22 axial cords, interstices with finest lamellar growth lines; first fine spiral thread after 1–2 axial cords, five at onset of selenizone. Teleoconch II of at least 1.75 whorls (based on shell remnants on base of holotype), shoulder with similar sculpture as on teleoconch I, about five spiral lines irregularly spaced between suture and selenizone. Selenizone slightly above periphery; keels of moderate strength, elevation. Base without constriction below selenizone, with axial cords similar to shoulder, spiral lines increasing in strength towards umbilicus, in vicinity of umbilicus forming small nodes at intersection with axial cords. Umbilicus narrow, distinct funiculus.

Comparisons. Sinezona malloryi ( Squires & Goedert, 1996) from middle early Eocene rocks in Washington has a distinct constriction of the base below the selenizone, and the suture is above the periphery of the previous whorl. Sinezona cupelliformis ( Amitrov, 1996) from Eocene strata of Ukraine has many more axials. Scissurella aliceae Schnetler, Lozouet & Pacaud, 2001 , from Paleocene rocks in Denmark has a sunken protoconch, a much wider selenizone, and stronger spiral sculpture on the shoulder. Scissurella bituminata Beets, 1942 , from Oligocene (or late Miocene, see Janssen 1999) deposits in Indonesia has a distinct constriction below the selenizone, and more distinct and regular spiral sculpture. Scissurella depontailleri Cossmann, 1879 , including its various synonyms ( Geiger 2012), of Paleocene through Miocene age from Europe has regular spiral sculpture on the base. Scissurella marchmontensis Sohl, 1992 , from Late Cretaceous rocks of the Caribbean has a distinct constriction on the base below the selenizone and prosocline axials.

Remarks. The generic assignment to Scissurella is tentative because no complete mature specimens are known. Protoconch sculpture had been considered a means to diagnose scissurellid genera, but it has been shown to be highly variable ( Geiger 2003, 2012).

Figures

FIGURE 1. Scisurella nesbittae new species, from type locality. A. Holotype SBMNH 467092. B–C. Paratypes SBMNH 637694. Scale bars shells = 1 mm. Scale bar protoconchs = 100 µm.