Mizuhopecten kavranensis Sinelnikova, 1975
SINELNIKOVA, V. N. 1975. Mio-Pliocene Pectinidae of
Kamchatka [Pektinidy mio-pliotsena Kamchatki]. Transactions of the Geological
Institute, Academy of Sciences of the USSR, 229: 1-140, 25 pls. (in
Russian with English title and contents). [p. 46, pl. 9, figs. 1, 2a, b, 3, 4a, b, 5, 6a-c, 7a, b; pl. 23, figs. 1a, b]
1975 Mizuhopecten kavranensis Sinelnikova, 1975
V. N. Sinelnikova, 1975, plate 9.
V. N. Sinelnikova, 1975, plate 23.
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«1938. Pecten (Patinopecten) yessoensis (part) Slodkevitsho PI. 32, fig. 2 P. 189
Holotype: GIN (National Geological Institute) AN USSR, No. 1434, Kamckatka, western beach, of Tigilskii region, sea beach at 2 km north of the mouth Kovran river, Kakert suite, bed with Kotorapecten Subrefugionensis. Diagnosis: Shell is large, whith radial ribs, inequivulve, except for the auricles it is nearly equilateral. Left valve is flat, rarely feebly convex or concave, with fine narrow sharply radial ribs. Right valve is convex, with radial riblets and with high radial ribs (19-22), with straight angle in cross section. Description: Shell is up to 10 cm in diameter, rounded, not strongly convex, beak not sharp, not reaching behined the ligament margin sufficiently broad, apical angle 115°. Lateral sides of the interstitial triangle are concave, but not strongly. In the younger forms they are nearly straight. Ligament area is slightly concave and auricles are nearly equal. The anterior is slightly larger than the posterior. Anterior auricle of the right valve has rounded anterior margin, wide, small and gentle byssal notch, with feebly concave fasciole, separated from the rest of the surfuce of the auricle by a low-acute crest. Anterior auricle is sculptured with broad round-taped radial ribs (from 4 to 5) with narrow intercostal intervals. Some ribs, especially near the fasciole, in the anterior end of the auricle, are doubled. Posterior auricle is obliquely-truncated, with feebly rounded margin, sculptured with very delicate, nearly unmarked radial ribs. Usually in worn out shell, the posterior auricle is smooth, with some concentric grooves of growth. All the surface of the shell is covered with narrow, raised, radial ribs (from 19 to 22), separated by narrow deep intercostal intervals. The lateral sides of the ribs are straight and the bottom of the intercostal interval is nearly flat. In pallial margin some radial ribs are split into 2. On the lateral slope of the disk, the radial ribs are less high, and split into 2 or 3 branches by shallow grooves. The left valve has a feebly concave ligament margin and high auricles of nearly equal length. Anterior auricle is a little higher and longer than the posterior one, covered with 8-9 radial ribs of different heights and widths, somehow obliquely-truncated and sometime slightly turned upward in the ligament. The posterior is also obliquely-truncated with feebly-marked radial sculpture. Apical angel is 110-115°. Interstitial triangle has feebly concave sides. The beak is sharp, feebly appears behind the ligament margin. Sculpture, from 19-22 radial ribs, is sometimes not of similar height, and usually between eacll two much higher and wider ribs lies, by one, much lower and narrower ones. The radial ribs in cross section are sharply-angled, narrow and slightly-split at the pallial margin, where they become higher and coarser. Intercostal intervals are flat. All the surface is covered with a delicate reticulated microsculpture. The reticulation is nearly straightly-angled. Pseudodental apparatus (fig 15) of the right valve consists of triangular resilifer and lies nearly in the center of the ligament area which is sufficiently deep and equilateral. Anterior lateral plate of the resilifer is narrow, short and equal. From top of the resilifer to the anterior end of the posterior and anterior auricles, the cardinal plates run gently inclined inward. The hinge groove in the anterior auricle is sufficiently broad, while it is shorter and nerrower in posterior. The cardinal plates on both auricles do not reach the end of the hinge area. In posterior auricle, the cardinal plate is 1/4 length of the auricle, steeply turns upward, closely reach the end of the hinge margin and delimited with a deep broad groove between it and the hinge margin. Pseudodental apparatus,of the left valve also consists of triangular resilifer, lying nearly in the center of the hinge area. Resilifer is not deep, smaller than in the right valve, and sufficiently narrow. At the end of anterior and posterior walls of the resilifer the dental lugs are slightly raised, above which a small groove lying in the lateral plates of the resilifer of the right valve. The grooves, at the top of the auricles, are broadened and extended downward. On the posterior auricle at the lower end of the resilifer, there is a feebly-marked groove. The cardinal pIates along the hinge margin are feebly inclined inward, not reaching the end of the auricle, about 1/4 of length. The groove of the cardinal plate of the right valve is deep and distinct.
Auricular plates are distinctly marked. In the anterior auricle they are double, in the posterior-single, without distal lugs. Dimensions: Length- 87 mm, height- 84 mm, convexity- 15 mm, length of the hinge margin about 50 mm. Comparison: M. Yessoensis is considered as the nearest species, from which species of Kamchatka is differentiated by much narrower ribs an the left valve, and their sharp top, straightly-angled reticulated microsculpture (in M. yessoensis-reticulum is obtusely-angled), Concave hinge margin, feebly-marked radial sculpture on the anterior auricle of the left valve, narrow intercostal intervals (in M. yessoensis intercostal intervals in width are nearly equal to ribs); much gentle and small byssal notch, with extending radial ribs in peripheral margin of the disk, and their small number. From M. Slodkewitsch, the described species is differentiated by a large number of radial ribs, their smaller width, very feebly-marked split ribs which are much broader and do not reach the beak; much lower aricles and dental lugs on the lower end of the lateral sides of the resilifer in the right valve. On the left one in M. Kavranensis, the ribs are much higher and sharper than in M. slodkevitsch; the hinge margin is slightly convex, while as in M. slodkevitsch it is straight; the groove for the cardinal plates is inclined downward, the goove is lees distinctly marked. Moreover, in the posterior auricle at the hinge margin, there is no oval deepening of the thickening of the cardinal plate of the right valve. Usually it is well developed in M. slodkewitsch. M. kitamiensis is considered as the least near, from which M. Kavransis is differentiated by a large number and much distinct branched-radial ribs on the right valve, considerably with much shorter anterior auricle and gentle small byssal notch. The left valve of M. Kavranensis is differentiated by a small convexity and large number of radial ripe and large apical angle. Material: 30 well-preserved shells, all the valves are broken. Location: Kamchatka, western beach, Tigilskii region, Kheisli River, (outcrop 24, bed 3, Sample 141), Sea beach at 2 km north of the mouth of Kovran River (section 8, bed 3), Sea shore some km north of the mouth of Mainash River sea shore to the south from the promontory Nepropusk (section 2, bed 4.). Distribution: Kovranskaya series, Kakert suite. Age: Upper (?) Miocene.» VALENTINA NIKOLAEVNA SINELNIKOVA, 1975
[Translated for the U. S. Department of the Interior, Geological Survey, and the National Science Foundation, Washington, D. C., by the Al-Ahram Center for Scientific Translations. 1977] |