Cardiomya anaticepsella, Carole & Hickman & Ca, 2014

Carole, Hickman, S. & Ca, 2014, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, part IV: The anomalodesmatans, PaleoBios 31 (3), pp. 1-21 : 14-16

Cardiomya anaticepsella n. sp.

Figs. 5A–D

Cardiomya n. sp. Vokes in Warren et al. 1945. (checklist)

Diagnosis —Shell of normal size for genus (length to 10 mm), with ovate, inflated disc and long, smooth, straight, compressed, posterior rostrum. Disc with 18 to 20 well-developed rounded radial ribs. Radial ribs on anterior disc finer than those on posterior segment. Coarser posterior ribs with wider interspaces with occasional finer interrib. Umbones situated posterior to midlength of inflated portion of valve, approximately at 1/3 total shell length. Interior and hinge features unknown.

Discussion —Shells of this species are thin but are not crushed as in the other Keasey anomalodesmatan taxa. They are readily distinguished from the other anomalodesmatans by the rostrate shell form, smaller size, lack of nacre (as in Pandora and Aperiploma ) or granules on the surface of the shell (as in Thracia ).

The only other Paleogene Cardiomya from the Pacific Northwest, C. comstockensis Turner, 1938 , has fewer radial ribs on the expanded disc and has radial ribbing on the rostrum, which is also proportionally shorter and broader. Species from the California Eocene that differ in having radial ribbing on the rostrum include three species from the Rose Canyon Shale originally described under Cuspidaria : C. russeli (M.A. Hanna, 1927) , C. israelskya (M.A. Hanna, 1927) , and C. vorbei (M.A. Hanna, 1927) , as well as C. silverensis Vokes, 1939 from the Domengine Formation. Cardiomya domenginica Vokes, 1939 lacks ribbing on the rostrum but is unique in a disc ornamentation of numerous very fine radial threads. Cardiomya hannibali ( Dickerson, 1914) from the Martinez Formation of northern California is distinguished by a disc divided into a smooth anterior portion and a posterior portion with four radial ribs and a rostrum bearing a single sharp thread extending from the beak to the distal end. Type specimens of all of the above species are in the UC Museum of Paleontology type collection, facilitating comparisons.

Preservation of this species is primarily as external and internal molds, and illustrations are primarily from latex casts coated with ammonium chloride.

Etymology —The name refers to the superficial resemblance of the shell outline to a miniature duck head and is the name that Harold Vokes attached to intended USNM type specimens.

Material examined —Diagnosis is based on 11 specimens. Seven of the specimens are from the main crinoidbearing layer at the Mist locality.

Holotype — USNM 561796 , left valve, length 10.5 mm, height 5.2 mm, Loc. USGS 15263 .

Paratypes — USNM 561796 , left valve, length 5.8 mm, height 3.8 mm, Loc. USGS 15263 ; USNM 561795 , left valve, length 7.8 mm, height 4.6 mm, Loc. USGS 15318 .

Keasey Formation localities — Type Locality: USGS 15263 (lower member). Other localities: USGS 15309 (lower member), USGS 15318 (middle member) .