Amano et al.—New and Mesozoic-relict mollusks from Paleocene wood-fall communities
Table 5. Measurements of Poromya katsuhiraensis Amano and Jenkins, n. sp. H=height, L=length,W=width, – = not available; + =dimension in slightly imperfect case.
Locality Specimen
Loc. 1 JUE 16006, holotype Loc. 1 JUE 16007-1, paratype
L (mm) H (mm) W(mm) Valve 7.2
Loc. 1 JUE 16007-2, paratype 7.8+ Loc. 1 JUE 16007-3, paratype Loc. 1 JUE 16007-4, paratype Loc. 1 JUE 16008
7.9 5.5
10.8 5.4 11.1
6.2 7.0 7.5 5.4 5.0
4.7 – –
3.7 3.5 –
both right left
both both right
from Loc. 1. Type locality: bank of the Urahoro River at the mouth of Kokatsuhira-zawa, Katsuhira in Urahoro Town, Hokkaido, Japan, 42°59’20”N, 143°38’04”E; Paleocene.
Diagnosis.—Moderate-sized and subquadrate Poromya with posterior carina from beak to posteroventral corner and rather deep groove just before posterior adductor muscle scar. Inner surface nacreous, covered with fine radial grooves in anterior disc before carina. Right valve with one cardinal; left valve with one socket.
Occurrence.—Upper Selandian to lowermost Thanetian, Katsuhira Formation, eastern Hokkaido, Japan.
Description.—Shell of moderate size (to 10.8mm L), rather thin, inequilateral, equivalve, subquadrate, slightly longer than high or higher than long (H/L= 0.86–1.03), moderately inflated (W/L=0.65–0.67). Anterodorsal margin concave; anterior margin subcircular; ventral margin broadly arcuated. Poster- odorsal margin nearly straight and gently sloping; posterior margin truncated. Beak prosogyrate and anteriorly situated at one-third L. Distinct carina running from beak to posteroventral corner, separating anterior and posterior parts of shell. Rather deep groove just before posterior adductor muscle scar and forming strongly concave posteroventral margin. Outer surface
poorly preserved; inner surface nacreous, sculptured by ~10 fine, weak radial grooves behind carina. One cardinal tooth of right valve small, inserting into socket of left valve. Pallial sinus very shallow, small, just before posterior adductor muscle scar. Anterior adductor muscle scar small, subovate; posterior adductor muscle scar of similar size and shape to anterior one.
Etymology.—Named after the formation at the type locality.
Materials.—Six specimens from the type locality, including one poorly preserved specimen (JUE 16008); see Table 5 for dimensions.
Remarks.—Poromya katsuhiraensis n. sp. is the oldest species of Poromya in the world. It is closely similar to the Recent species P. carinata Lan, 2000 from the Dongsha Islands of Taiwan in size (8.8mm L in P. carinata) and in having a pro- minent carina. However, P. katsuhiraensis n. sp. can easily be distinguished from P. carinata by its rather deep groove just before the posterior adductor muscle scar, no groove before the carina, and a longer, truncated posterior margin. The prominent carina distinguishes the present species from the two fossil species P. osawanoensis Tsuda, 1959, from the uppermost
641
lower to lowermost middle Miocene Kurosedani Formation in Toyama Prefecture, and P. yasuokana Nomura and Hatai, 1936 from the upper Miocene Kubota Formation in Fukushima Prefecture.
Class Gastropoda Cuvier, 1795 Subclass Caenogastropoda Cox, 1960
Order Littorinimorpha Golikov and Starobogatov, 1975 Family Naticidae Guilding, 1834
Subfamily Polinicinae Finlay and Marwick, 1937 Genus Neverita Risso, 1826
Type species.—Neverita josephinia Risso, 1826 (by original designation); Eocene to Holocene, Europe.
Neverita majimai Amano and Jenkins, new species
urn:lsid:
zoobank.org:act:0EA3A33A-4B9F-4A14-A3D6- D13034D25993
Figure 4.1–4.7, Table 6
Type specimens.—Holotype, JUE 16018, from 500m upstream of Katsuhira-kita-zawa, Urahoro Town, Hokkaido (Loc. 15); paratypes, JUE 16019-1–2, from the type locality; paratype, JUE 16020, from 480m upstream of Katsuhira-kita-zawa (Loc. 16); paratype, JUE 16021, from 325m upstream of Katsuhira-zawa (Loc. 28). Type locality: 500m upstream of Katsuhira-kita-zawa, Urahoro Town, Hokkaido, Japan, 42°59'27''N, 143°38'43''E; Paleocene.
Diagnosis.—Small globose Neverita with 4.5 whorls including 1.5 whorls of low-spired protoconch, low spire, and large, massive, semicircular umbilical callus, completely covering umbilicus. Umbilical callus sculptured with weak groove in central part and some very weak furrows on both sides of groove. Surface smooth except for weak axial wrinkles in weakly depressed subsutural area on last whorl.
Occurrence.—Upper Selandian to lowermost Thanetian, Kat- suhira Formation, eastern Hokkaido, Japan.
Description.—Shell small for genus (to 11.5mm H), globose, thin, with low spire; of 4.5 whorls including planispiral proto- conch (1.6mmD) of 1.5 whorls; suture shallow; subsutural area slightly depressed, with weak vertical growth wrinkles; shallow furrow separating substural depressed area on last whorl. Surface smooth except for subsutural wrinkles and growth lines. Parietal callus thin. Umbilicus completely covered with massive semicircular umbilical callus with one weak, central transverse groove; several very weak furrows on both sides of groove. Outer lip thin; interior lip moderately thick.
Etymology.—Named after Prof. Ryuichi Majima (Yokoyama National University) who studied the taxonomy of Cenozoic naticids in Japan.
Materials.—Five specimens from the type locality (Loc. 15); one specimen from 480m upstream of Katsuhira-kita-zawa (Loc. 16); four specimens from 325m upstream of Katsuhira- zawa (Loc. 28); two specimens from 450m upstream of
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