Indopecten seinaamensis (Krumbeck, 1924)
KRUMBECK, L. 1924. Die Brachiopoden, Lamellibranchiaten und Gastropoden der Trias von Timor II. Paläontologischer Teil. Paläontologie von Timor, 13 (22): 1-275, Taf. 1-20, Stuttgart (Schweizerbart) [p. 202, pl. 143 (15), figs. 10-12]
1924 Pecten (Aequipecten) subserraticosta Krumbeck, 1924 [partim]
1924 Pecten (Aequipecten) seinaamensis Krumbeck, 1924
1924 Pecten (Aequipecten) seinaamensis Krumbeck, 1924
1924. Pecten (Aequipecten) seinaamensis Krumbeek, 'Pal. Timor' vol. xm, pt. 22, pl. cxciii, figs. 10-12 & p. 344.
1924. Pecten (Aequipecten) subserraticosta (pars) Krumbeek, ibid. pl. cxciii, fig. 7. This species, the original description of which was based on right valves alone, is abundantly represented in the collection here described, many of the specimens retaining the two valves intact.
A more complete diagnosis than that given by Krumbeck is, therefore, possible. Specific characters.— Shell of variable shape, subcircular to obovate, inequivalve.
Right valve moderately convex, with five prominent broadly-rounded ribs or folds, and in the young shell an additional anterior and posterior rib of almost equal strength. These main folds bear a variable number of minor ribs, of which three or more of the central rows on each main fold bear small rounded knots or tubercles set at regular intervals. The strength and number of these minor ribs, which are the chief diagnostic feature of the species, are a very variable factor, and a complete gradation can be traced from forms with three rows of knots (as in Krumbeck's type-specimen), to one in which each of the main folds bears at least a dozen minor ribs, all of which bear knots, especially towards the ventral margin. In this extreme instance it is hard to differentiate between folds and furrows, for the minor ribs are as prominent in the one as in the other, and there is scarcely any sign of a median break along the axis of the furrows. Concentric growth-striae are very numerous and evenly spaced, and these, crossing the minor radial ribs, especially when the latter are numerous, give a reticulate appealance to the ornament. Left valve plane-convex, with six prominent subangular folds separated by broad subangular furrows. These folds hear, as a rule, one median row of tubercles, but may have as many as five rows, which, however, are not borne on continuous ribs, so that the reticulate ornamentation seen in the right valve is lacking. The tubercles on the posterior fold are set obliquely to the axis, as in Pecten clignetti. This valve has the zigzag internal shellstructure characteristic of the subgenus. Remarks.— The foregoing description of the characters of the left valve is based on specimens wit h the two valves intact, and I am led to put forward the suggestion that at least one of the specimens of P. subserraticosta, described by Krumbeck as a distinct species, is in reality only the left valve of P. seinaamensis, for, if possessed of left valves alone, I should unhesitatingly have referred them to the former species. Of Krumbeck's figures (op. cit. pl. cxciii) no. 7, although described as a right valve, is clearly a left valve, for it shows traces of zigzag shell-structure, and it is inseparable from the left valves of several of my specimens.
Although I have not included it in the list of synonyms, it is probable that Lima (?) serraticosta Bittner (1899, pl. viii, fig. 12) is also a left valve of this species. Comparison with other species.— Although the actual number of rows of knots on a fold cannot be regarded as a specific distinction, Indopecten seinaamensis is distinguished from Pecten clignetti Krumbeek by the presence in the left valve of the latter of broad flattened furrows bearing subsidiary ribs.
The two are, however, closely related species. DOUGLAS, J. A. 1929. A marine Triassic fauna from eastern Persia. The Quarterly Journal of the Geological Society of London, 85: 624-648, pls. 42-46. [p. 633.635]
|
Indopecten seinaamensis (Krumbeck); J. A. Douglas, 1929, A marine Triassic fauna from eastern Persia, plate 44, figures 1, 4, 5.
|