Praespondylopecten besnossowi Romanov, 1987
KASUM-ZADE, A. A. & L. F. ROMANOV. 1987. Spondylopectinidae Kasum-Zade & Romanov, fam. nov. of Jurassic in the south of the USSR. In: L. A. Nevasskaya (Ed.), Stratigraphy of the Moldavian Upper Phanerozoic. Shtiinstsa, Kishinev: 6-16, pl. 1, 2 (in Russian). [p. 14, pl. 2, figs. 10-12]
1987 Praespondylopecten besnossowi Romanov, 1987
A. A. Kasum-Zade & L. F. Romanov, 1987, plate 2
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«Holotype. Praespondylopecten besnossowi sp. nov. Collection M-8/230. Lower Jurassic of the northern Caucasus, Pleinsbachian stage.
Description. Shell small, rounded oval, inequivalved. Right valve is flat, left is relatively convex, with beak protruding over hinge margin. Hinge margin straight. Auricles unequal: anterior is relatively larger and with deep byssal notch. Apical angle is obtuse. Dimensions: height: height: 8.10, length: 7.70 mm; anterior auricle: 3.75, posterior: 2.75 mm; < = 96°. Right valve is relatively flat, with central beak, situated at level of hinge margin. Auricles not equal: anterior is larger and is with deep byssal notch. Hinge margin straight. On the inner surface along the margins of the resilifer are two large odontoid processes, the posterior of which is larger (is traced on two specimens). The inner surface of the valve is smooth. Muscle impression is large, and is situated in posterior part of valve. Pallial margin is crenate. Outer sculpture is represented by 14 radial ribs, straight, rounded-tetragonal with interspaces narrower than ribs. On the margins is situated a single radial fold each. Auricles as well are covered by radial ribs, relatively coarse. Entire surface of valve is covered by concentric growth lines, which are traced as well in the interspaces. In the lower part of the valve, growth lines are coarser, and in some specimens, the lower part of valve recurves inward. Left valve differs from the right in having “stronger” convexity, slightly protruding beak. As in the right valve, the left consists of 14 radial ribs, thinner {finer}, with interspaces twice as wide as the ribs. One fold is present on each of the margins of the valve. Concentric lines cover the entire valve, but in difference from the right, they are more clearly manifested in the rib interspaces. Comparisons and comments. The presence of two odontoid processes on the hinge margin of the right valve make this species incomparable with some species of the genus Pseudopecten, to which the structure of the outer surface of both valves is similar. In external morphological characters it is very closely related to, and even indistinguishable from, Pseudopecten (Pseudopecten) priscus (Schlot.). The appearance of the shell and the identical sculpture differing on the right and left valves brings them together. In P. (P.) priscus (Schlotheim) there are 20 radial ribs, but in P. besnossowi, there are 14, 16 when counting lateral folds. However, Staesche (1926) also attributed to P. (P.) priscus (Schlotheim) forms with 16 radial ribs. It is not to be excluded, that the mentioned forms belong to the species being described {here}. Range and age. USSR: northern Caucasus. Lower Jurassic, Pliensbachian stage. LEONID FEDOROVICH ROMANOV, 1987
[Translated by Rosanne D’Aprile Johnson, VIARC, Smithsonian Institution, 8 August 2007] |