Pecten kakisakiensis Nomura & Niino, 1932
NOMURA,
S. & H. NIINO. 1932. Fossil Mollusca from Izu and Hakone. Science
Reports of the Tohoku University [2nd. Series - Geology], 15 (3):
169-192, pls. 11, 12. [p. 177, pl. 12, figs. 3, 4]
«Pecten kakisakiensis n. sp.
PI. XII (II), Figs. 3, 4. Shell medium in size, compressed, somewhat higher than long, equivalve, equilateral except for ears; sides sloping, very slightly concave above or almost straight; umbonal angle 85°; test rather thin. Right valve with 26 equal, rounded, more or less scaly ribs which are subsequently divided into three unequal parts as the shell grows; median one is largest, the other two
smaller and equal; interspaces narrower than ribs and rarely with an interstitial riblet near the ventral margin in a well grown specimen. Ears unequal; anterior ear being longer and larger than the posterior; byssal notch prominent, rather deep and its end rounded; posterior ear nearly rectangularly truncated; both ears sculptured by 6 radial scaly riblets. Hinge line more than one-half of disk-length. Left valve nearly similar to the right, except for ears. The anterior ear being smaller than the posterior, obliquely truncated. Dimensions : — Height, 55 mm.; length, 53 mm.; depth, ca. 6 mm. Length of ear, 29 mm. (a right valve). This species somewhat resembles P. nobilis RVE., a species found as fossil and living in Japan, but it is distinguished from that species by the ribs. In P. nobilis the ribs are simple and usually 23 or 24 in number while in the present species there are 26 ribs and each of them accompanies riblets on both sides. Pecten kakisakiensis n. sp. is more closely allied to P. satoi YOKOYAMA¹ from the Island of Taiwan; the difference between the two is in the less number of ribs in the present species. P. satoi is said to have 30 ribs according to Dr. YOKOYAMA. Occurrence : -- Kakisaki (Shirahama Group).» ¹YOKOYAMA, M.: Imp. Geol. Surv. Jap., Rep. No. 101, 1928, p. 94, PI. XIII, figs. 13, 14; PI. XIV, fig. 2. SHICHIHEI NOMURA & HIROSHI NIINO, 1932
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S. Nomura & H. Niino, 1932, plate 12.
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