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Pachydiscus (Pachydiscus) jacquoti Seunes 1890 from: Kennedy, W.J.. (1986): The ammonite fauna of the Calcaire à Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France) . Palaeontology Vol. 29(1) p. 25-83
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Species Pachydiscus (Pachydiscus) jacquoti Seunes 1890



Alternative name:
Diagnosis / Definition:
Kennedy (1986):
Types. Seunes figured three specimens (1890a, pI. 3 (2), figs. 1-3) and mentioned aseries of other specimens from the Pyrenees-Occidentales (now Pyrenees-Atlantiques) (possibly those figured by hirn in 1890b, pl. 9, figs. 1-4) as weIl as a specimen from north-west of Alcoy, Alicante, Spain; all are syntypes ofthe species. I have been unable to trace the original ofhis pI. 3 (2), fig. 1, which was in the Janet Collection, nor the original ofhis pI. 3 (2), fig. 2, said to be in the EMP Collections. The original ofhis fig. 3 survives in the latter collection (unreg.) but is the smallest ofthe three (PI. 9, fig. 7) and does not show the characteristic adult features ofthe species. I hesitate to designate a lectotype in these circumstances. If the original of Seunes (1890a, pI. 3 (2); fig. 1) is located, it should be designated lectotype. Material. BMNH C38175 from Fresville; BMNH C38177 and C70625, parts ofthe same specimen but labelIed 'Fresville' and 'near Valognes' respectively (all J. Sowerby, ex de Gerville Collection); FSR 7 from Fresville (Seunes Collection); FSR 8-10, labelIed 'Manche'. The original ofSeunes (1891, pI. 12 (3), fig. 4), originally in the de Lapparent Collection (formerly in the Institute Catholique, Paris), has not been traced. Description. All specimens are internal moulds of juvenile phragmocones; no adult body-chambers are known from the Cotentin. Coiling moderately evolute (U = 30• 7 -32' 7%), whorls expanding slowly. Umbilicus shallow, with rounded, outwards-incIined wall. Umbilical shoulder broadly rounded, inner flanks broadly rounded, outer flanks flattened and convergent, venter broadly rounded. Whorl section slightly depressed intercostally up to a diameter of 70 mm, thereafter slightly compressed. Greatest breadth at umbilical bullae at all diameters. Shell initially smooth (pI. 5, figs. 15 and 19). Weak umbilical bullae, four per half whorl, first appear at a diameter of 12 mm, and are only ornament up to diameter of35-45 mm (pI. 5, figs. 9-11; PI. 9, fig. 7) where they number up to eight per whorl. Ornament thereafter (Seunes 1890a, pI. 2 (3), fig. 2; de Grossouvre 1894, pI. 26, fig. 3) shows bullae elongating into pairs of narrow and distant prorsiradiate ribs; shorter intercalated ribs also appear, Overall rib density increases, with thirteen or fourteen bullae at a diameter of 70 mm (pI. 6, fig. 2) and twice this number of ribs at ventrolateral shoulder. Ribs weaken over venter, interrupted by a narrow groove over siphonalline. Secondary ribs decline beyond 90 mm, and in largest specimen seen (PI. 6) there are fifteen umbilical bullae at 122 mm diameter which become progressively wider spaced over last halfwhorl, where they give rise to single ribs that decline on flank and virtually disappear over venter. Secondary ribs weaken arid eventually disappear by same diameter. What I take to be the adult body-chamber (Seunes 1890h, pI. 9, fig. 4) has distant primary ribs only. Suture (text-fig. 4B) is intricately subdivided, with large externallobe, deep E, large asymmetrically bifid EIL, deeplyincised bifid L and U2, and smaller asymmetrically bifid L/U2.
Discussion / Comments:
Kennedy (1986):
Discussion. De Grossouvre (1894, p. 207) erred in uniting this species with P. neubergicus Hauer, 1858 (pI. 4, fig. 3), which has a compressed oval whorl section whenjuvenile. Although also omamented by umbilical bullae which give rise to primary ribs only, these are coarser, blunter, and more numerous. In middle growth, as represented by the lectotype (Hauer 1858, p. 12 (pars), pI. 2, figs. 1-3 only) (see PI. 4, fig. 3), Hauer's species is more involute, with more numerous primary ribs and bullae and many short secondaries and intercalatories on ventrolateral shoulders and venter. At maturity, topotypes of P. neubergicus lose all but umbilical bullae and primary ribs that efface on the outer flank. P. jacquoti is much more evolute and coarser ribbed than P. gollevi/lensis, and lacks the fine, dense, ventral ribbing ofthat species. It should be noted that d'Orbigny's smaller figured specimen (1841, pI. 102, figs. 1 and 2) is a juvenile jacquoti. Perhaps the closest ally of P.jacquoti is P. egertoni (Forbes, 1846a) (p. 108, pI. 9, fig. 1), ofwhich P. ganesa (Forbes, 1846a) (p. 103, pI. 7, fig. 8) is a synonym. The type material is from the Maastrichtian Valudayur Beds ofPondicherry, southern India, and the specimen figured by Forbes (BMNH C51038) is here designated lectotype, The species differs from Pi jacquoti (which Atabekian and Akopian 1969 regarded as no more than subspecifically distinct) in having weaker ornament (effaced on the venter), a smaller umbilicus, higher compressed whorls with strongly convergent flanks, and a narrow arched venter with ornament declining from a much smaller diameter. Kossmat's specimen (1898, p. 94 (159), pI. 15 (21), fig. 4a-c) may be ajacquoti, however. P.j. australis Henderson and McNamara, 1985 (p. 76, pI. 8, figs. 1,2,7-10; text-figs. 12a, 13b, 14, 15a) is a coarser ribbed form that retains its secondary ribs to a large diameter (see also Wetze11930, p. 85, pI. 13, fig. 2).
Synonym list:
Kennedy (1986):
1840 Ammonites lewesiensis Mantell. - Orbigny : 336 (pars) pl. 102, figs. 1 and 2
1850 Ammonites gollevillensis d'Orbigny. - Orbigny : 212 (pars)
1861 Ammonites colligatus Binkhorst. - Binkhorst : 25 (pars) pl. 6, fig. 3a-f(?); pl. 7, fig 2a,b only
1890 Pachydiscus jacquoti Seunes. - Seunes : p.5 pl. 3(2), figs. 1-3
1890 Pachydiscus jacquoti Seunes. - Seunes : p.237 pl. 9, figs. 1-4
1891 Pachydiscus jacquoti Seunes. - Seunes : p.9 pl. 12 (3), fig. 4
1894 Pachydiscus neubergicus Hauer. - Grossouvre : 207 (pars) pl. 26, fig. 3; pl. 38, fig. 3 sp. emend., A. de Grossouvre
1908 Pachydiscus neubergicus Hauer. - Grossouvre : p.30 pl. 9, figs. 3 and 4 sp. emend., de Gross
1938 Pachydiscus neubergicus Jacquoti Seunes. - COLLIGNON : 48 (98) pl. 11, fig. 1
? 1952 Pachydiscus cf. pachydiscus jacquoti Seunes. - USHER : p.72 pl. 11, figs. 1-3; pl. 31, fig. 1
1969 Pachydiscus egertoni jacquoti Seunes. - ATABEKIAN & AKOPIAN : p.9 pl. 1, fig. 3; pl. 2, fig. 2; pl. 4, fig. 1
1971 Pachydiscus jacquoti Seunes. - COLLIGNON : p.36 pl. 655, figs. 2412 and 2413
1986 Pachydiscus (Pachydiscus) jacquoti Seunes. - Kennedy : 34 pp. pl. 5, figs. 3-11, 15-19; pl. 6; text-figs. 2D, E, 3O, S, 4B
Was used in synonym list of:
Stratigraphy - relative ages:
upper Maastrichtian - Maastrichtian: Kennedy (1986)
References:

Orbigny,A.D.. (1840):
1840-1842. Paleontologie francaise: Terrains cretaces. 1, Cephalopodes. p. 1-120 (1840),12

Orbigny,A.D.. (1850):
Prodrome de Paleontologie stratigraphique universelle des animaux mollusques et rayonnes. Vol. 2 p. 428 pp.

Binkhorst,J.T.. (1861):
Monographie des gastropodes et des céphalopodes de la Craie Supérieure du Limburg.
In: Maastricht and Muller Frères Eds: Muquardt, G.. p. 17,83,44

Seunes,J.. (1890):
Recherches géologiques sur les terrains secondaires et l' Eocene inferieur de la region sous-pyrénéene du sud-ouest de la France (Basses-Pyrenees et Landes). p. 250 pp.

Seunes,J.. (1890):
Contribution a l'etude des cephalopodes du Cretace Superieur de France. 1. Ammonites du Calcaire ä Baculites du Cotentin. . Mém. Soc. geol. Fr. Paleont. 1, Mém. Vol. 2 p. 1-7

Seunes,J.. (1891):
Contributions à l’étude des Céphalopodes du Crétacé Supérieur de France. Ammonites du Calcaire à Baculites du Cotenin (Suite); II. Ammonites du Campanien de la région sous-Pyrénéenne, Département de Landes . Mémoirs de la Société Géologique de France, Paléontologie Vol. 2(2) p. 8-22

Grossouvre,d.A.. (1894):
Recherches sur la Craie Supérieure, 2, Paléontologie. Les ammonites de la Craie Supérieure, Mémoirs pour Servir à l’Explication de la Carte géologique détaillée de la France (mis-dated 1893).. p. 264

Grossouvre,d.A.. (1908):
Description des ammonites du Cretace Superieur du Limbourg Belge et Hollandais et du Hainault . Mem. Mus. r. Hist. nat. Belg Vol. 4 p. 1-39

COLLIGNON,M.. (1938):
Ammonites Campaniennes et Maastrichtiennes de I'ouest et du sud de Madagascar. . Annales Geologiques du Service des Mines de Madagascar Vol. 9 p. 55-118

USHER,J.L.. (1952):
Ammonite faunas of the Upper Cretaceous rocks of Vancouver Island . Bulletin of the Geological Survey of Canada Vol. 21 p. 1-182

ATABEKIAN,A.A.. and AKOPIAN,v.T.. (1969):
Late Cretaceous ammonites of the Armenian SSR (Pachydiscidae). . Proceedings of the Armenian Academy of Science, Earth Sciences. [In Georgian]. Vol. 6 p. 3-20

COLLIGNON,M.. (1971):
Atlas des fossiles caracteristiques de Madagascar (Ammonites)(Maestrichtian). Vol. 17 p. 82

Kennedy,W.J.. (1986):
The ammonite fauna of the Calcaire à Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France) . Palaeontology Vol. 29(1) p. 25-83

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