Masudapecten tryblium (Yokoyama, 1925)
YOKOYAMA, M. 1925. Tertiary Mollusca from Shinano and Echigo. Journal of the Faculty of Science, Imperial University of Tokyo [Section II: Geology, Mineralogy, Geography, Seismology], 1 (1): 1-23 [p. 17, pl. 6, figs. 1-2; pl. 7, figs. 1, 5]
1925 Pecten tryblium Yokoyama, 1925
1962 Patinopecten (Patinopecten) tryblium shinshuensis Akiyama, 1962
1962 Patinopecten (Patinopecten) tryblium shinshuensis Akiyama, 1962
M. Yokoyama, 1925, plates 6, 7.
|
«Shell somewhat larger than the preceding [Pecten yamasakii, n. sp.], rather thin, compressed, little longer than high, inequivalve, radiately ribbed, ribs a little over twenty in number. Right valve flatly convex with ribs, broad, elevated, broader than intervals, usually with a longitudinal groove in the lower two-thirds of the shell dividing them into equal or unequal parts, though occasionally it is either absent or so well developed and deep as to divide the ribs into two, save near beak; intervals smooth. Left valve almost flat with ribs narrow, ridge-like with intervals broader in which an intercalary riblet may sometimes be present; in one specimen a fine reticulate structure covers the surface. Ears equal in the left valve, unequal in the right in which the anterior is marked by a shallow notch below; radiately costellate. though sometimes quite indistinct. Length taken as 10, height 8.7-8.8, while depth is in the right valve 1.5, in the left not quite 1.
The largest example is 155 millim. long. This species is closely related to Pecten healeyi Arnold (Tert. a. Quatern. Pectens of California, p. 103, pI. XXXVI, fig. 1, 1a, pI. XXXVII, figs. 1, 1a, 2) in which the shell is higher and all the ribs are bipartite. Moreover the appearance of an intercalary rib in the left valve is regular, and the hinge-line comparatively shorter. Several specimens. Fossil occurrence.— Shigarami and Sakae.» MATAJIRO YOKOYAMA, 1925
|
«Shell moderate, rather thin, suborbicular, inequivalved, equilateral except for auricles, height nearly equal to length.
Right valve much convex, straight in side sloping, provided with 20-23 roundtopped, subequal, straight ribs which become obsolete towards submargins; interspaces much narrower than ribs themselves, concentric lines are weak and become distinct towards the ventral margin; anterior auricle sculptured with fine concentric striations and provided with conspicuous byssal notch; posterior one as large as the anterior, sculptured with fine concentric lines; hinge straight, with conspicuous cardinal crura and resilial pit provided with lateral ridges on both margins. Left valve much different sculpture from the right, a little convex, provided with 19-21 narrow elevated radials which become obsolete towards submargins; interspaces much broader than ribs themselves; both interspaces and radials with several, unequal radial threads on the lower half of the disc; on the other hand, its upper half with reticulate structure; concentric striations distinct; auticles triangular, sculptured with conspicuous concentric striations and inconspicuous threads; hinge straight with cardinal crura and resilial pit with shallow furrows on both margins corresponding to the said ridges of the right valve. Remarks. It can be stated that this species is sympatric with P. yamasakii yamasakii, being yielded from the upper most part of the Arakura pyroclastics, associated with yamasakii. Comparisons. The present subspecies is allied to P. yamasakii yamasakii, but can be distinguished therefrom by the right valve with undivided radials and the left valve with also undivided radials and numerous intercalaries P. yessoensis is related to the present species, but can be distinguisheg from the latter by the different sculpture of the left valve. Type locality. Exposure along the River Susobarra at Shimosoyama Shigaramimura, Kami-Minochi-gun, Nagano Prefecture. Upper most part of the Arakurayama pyroclastics. Reg. no. 17019 (topotype). Distribution. Arakurayama pyroclastics, and Ikari sandstone along the River Dojiri, both in Nagano Prefecture and Hirayama formation in Tokyo-to.» AKIYAMA, M. 1962. Studies on the phylogeny of Patinopecten in Japan. Science Reports of the Tokyo Kyoiku Daigaku [Section C - Geology, Mineralogy and Geography], 8 (74): 63-122, pls. 1-8, text-figs. 1-3. [p. 97, 98]
|
Patinopecten (Patinopecten) tryblium tryblium (Yokoyama); M. Akiyama, 1962, Studies on the phylogeny of Patinopecten in Japan, plate 5, figure 3.
|