Knemiceras gracile H. DOUVILLÉ , 1916

Latil, Ouvillé Ataller Jean-Louis & Aly, Mohamed Fouad, 2012, Knemiceras gracile D, 1916: a misunderstood Early Albian ammonite from north Sinai (Egypt), and considerations on the genus Platiknemiceras B, 1954, Revue de Paléobiologie 31 (1), pp. 159-170 : 160-161

Knemiceras gracile H. DOUVILLÉ, 1916

Figs 1, 2

1916. Knemiceras gracile H. DOUVILLÉ , p. 128, pl. 16, fig. 9; text-fig. 42.

? 1940. Engonoceras gracile DOUVILLÉ H. - BASSE, p. 438, pl. 4, fig. 1; text figs 9, 10.

1956. Knemiceras gracile H. DOUVILLÉ, 1916 .- MAHMOUD, text-fig.15.

? 1956. Knemiceras aff. gracile H. DOUVILLÉ. - MAHMOUD, p. 66, pl. 4, fig. 6.

non 1956. Knemiceras gracile H. DOUVILLÉ, 1916 .- ARNOULD- SAGET, p. 16, text-fig. 10; pl. 3, figs 3, 4.

1961. Platiknemiceras gracile DOUVILLÉ. - CASEY, p. 354.

non 2006. Knemiceras gracile DOUVILLÉ, 1916 .- ABU- ZIED, fig. 2r, pl. 6, figs 10-12.

non 2008. Knemiceras gracile DOUVILLÉ, 1916 .- ABU- ZIED, figs 2R, 7A-C.

Holotype: The holotype by monotypy is the specimen figured by H. DOUVILLÉ (1916, pl. 9, text-fig. 42), from NW of Talat el Fellahin (now Gabal Maaza), SE of Gabal Maghara, north Sinai, Egypt. The holotype, herein refigured ( Figs 1, 2), is deposited in the paleontological collections of the Université Claude-Bernard, Lyon as FSL.EM.1788 (former collections of the École des Mines de Paris ).

Dimensions of the holotype:

FSL.EM.1788: D: 53.0 (100) – Wh: 30.0 (57) – Wb: 16.0 (30) – U: 5.0 (9) – v: 2.4 (5) – Wb/Wh: 0.53 FSL.EM.1788: D: 70.0 (100) –Wh: 38.0 (54) – Wb: 21.0 (30) – U: 6.5 (9) – v: 3.7 (5) – Wb/Wh: 0.55 Description: A single specimen preserved as calcareous internal mould of a subadult phragmocone, 70 mm in diameter, with an estimated total diameter of at least 140 mm. The discoidal shell shows involute coiling with

1 cm

a very narrow umbilicus, comprising 9% of the diameter. The umbilicus increases in diameter on the last stages of ontogenesis, as suggested by traces on the flanks of the last whorl of the phragmocone. The umbilical wall is shallow and vertical with sharp umbilical shoulder. The whorl section is compressed, subtriangular (Wb/ Wh between 0.53 and 0.55), with maximum width at about the inner third of the flanks. The flanks are gently convex, converging to a very narrow venter (ventral thickness comprising less than 5% of the diameter). The ventral area is grooved and smooth, limited by rows of weak ventrolateral bullae, forming sharp, crenulated ventrolateral edges. The lateral ornament is almost nonexistent and restricted to weak, broad, coarse, regularly alternating primary and intercalatory ribs, up to a diameter of 40-50 mm. The ribbing style, while not well expressed, is characteristic of the genus. Beyond 50 mm in diameter, the lateral ribbing becomes inconspicuous, and tends to disappear altogether. The body chamber is unknown from the holotype. The suture shows entire saddles and feebly indentated lobes ( Fig. 2).

Discussion: This species remains poorly known, but seems to represent a primitive morphology of the genus Knemiceras BÖHM, 1898 , characterized by an almost lack of lateral ornament, a very narrowly grooved ventral area, and a suture with entire saddles and feebly indentated lobes.

The holotype seems to co-occur with an unequivocal juvenile representative of the genus Douvilleiceras de GROSSOUVRE, 1894 ( DOUVILLÉ, 1916, p. 120; pl. 15, fig. 7). MAHMOUD (1956: p. 66) does not provide details about the locality or stratigraphic level of the specimen he figured, but MORET & MAHMOUD (1953, p. 268 and 269) mentioned the species within their Levels 2 and 4, indicating an Early Albian age.

The specimens figured by BASSE (1940, pl. 4, fig. 1; textfigs 9, 10), from an unknown stratigraphic level of the Albian of Mdereidj, Lebanon, seem to be close to the present species by their general shape, suture and narrow concave ventral area, but the photographed specimen, herein figured ( Fig. 3) is too weathered and corroded to be specifically identified.

The specimens figured by ARNOULD- SAGET (1956, p. 16, text-fig. 10; pl. 3, figs 3, 4), from the Early Albian of southern Tunisia, are too weathered to be fully identified. Furthermore, the Tunisian specimens have a wider and flatter ventral area, and less convex flanks than the holotype .

ABU- ZIED (2006, fig. 2r, pl. 6, figs 10-12; 2008, figs 2R, 7A-C) mistakely figured a single specimen from El Tourkumanyia, north Sinai, Egypt, as Knemiceras gracile . The figured specimen, showing strong ribbing, wide umbilicus, pronounced umbilical tubercles, wide flat venter, and frilled suture. These morphological features seem to fall within the variability of Knemiceras spathi MAHMOUD, 1956 , rather than Knemiceras gracile DOUVILLÉ, 1916 . Therefore, the Knemiceras gracile biozone of ABU- ZIED (2008) is not herein accepted and needs to be revised.

Occurrence: Gabal Maaza, SE of the great Maghara Dome, north Sinai, Egypt, Early Albian. This species is doubtfully reported from the Albian of Mderedj, Lebanon.