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Species Diplomoceras lambi Spath 1953

Diagnosis / Definition:
SUPPLEMENTARY DESCRIPTION.- Shell of almost circular cross section (Figure 16, Table 4). Ornamentation composed of regularly spaced ribs that vary from straight to strongly oblique. The number of ribs at a distance on the flank equal to a diameter varies from 10 to 16. Suture line with E relatively narrow; first lateral lobe (L) deep, bifid, and extended laterally. Antisiphonal lobe less incised than L. The internal saddles are fused at the base to form a narrow stemmed saddle (Figure 15).
Discussion / Comments:
HOLOTYPE.- Diplomoceras lambi Spath, 1953, P1. 3, fig. 1 (BM.C41400), from the Naze, James Ross Island. MATERIAL.- 25 individual fragments, some more than 35 cm long, and usually with the original shell preserved. REMARKS.- This species is directly related to Diplomoceras notabile Whiteaves from Vancouver, Canada, and originally this material was included by Kilian and Reboul (1909) in that species. However, the species differ in the shape of the cross section (circular in D. lambi, and slightly oval in D. notabile). Also the suture line in D. lambi has less finely divided terminations, particularly terminations of saddles which are broadly rounded and expanded in this species and much more pointed in D. notabile. This is particularly clear when comparing the suture line figured here with that figured by Jones (1963, Fig. 15). Differences between D. notabile and D. cylindraceum (Defrance) from the Maastrichtian of Europe (i.e., Schlüter, 187 1-72, P1. 31, figs. 10-1 1) are not clear and they may be synonyms (Whiteaves, 1903, p. 336). Diplomoceras australe Hünicken (1 965, p. 67- 70, P1. 4, fig. 1) (as was observed in a cast preserved in the British Museum) and D. notabile (in Lahsen and Charrier, 1972, P1. 2, figs. 1-2) appear to be deformed, and they may represent flattened specimens of D. lambi. The status of D. lambi in relation to D. cylindraceum (Defrance) is not clear. Spath (1953) separated D. lambi from D. cylindraceum on the presence of a circular cross section in the former, and the smaller number of ribs in the latter (11 in a length equal to a diameter). Original specimens of the European species were not available for this study. However, D. cylindraceum apparently also has a circular cross section (implied by Birkelund, 1965, p. 67, and Wiedmann, written commun., 1984). Additionally, the new material from Seymour Island shows a ribbing pattern very similar to that of D. cylindraceum. Further studies, including a revision of the European material, may prove the identity of these two species. Until such a time, it is chosen to provisionally maintain D. lambi as a separate species. LOCALITES.- Seymour Island 4 1, 65, 99, 101, 160, 179, Loc. C, Loc. D, 322,336,338, 340, 347, 394,400, 410, St. 5, St. 6 and float between 37 and 60; Vega Island (Lots' V-9 and V-4); and also The Naze and Dagger Peak (James Ross Island) @path, 1953) and Snow Hill Island (Kilian and Reboul, 1909). STRATIGRAPHIC DISTRIBUTION.- Diplomoceras cylindraceum (the type species of the genus) was found in the Maastrichtian of Europe and its occurrence extends to the uppermost beds of the Maastrichtian chalk of Denmark (Birkelund, 1979). In Alaska, D. notabile was found in the Pachydiscus kamishakensis Zone of Jones (1963), which is believed to represent a lower Maastrichtian age. In the James Ross Basin this species has a long stratigraphic range, extending from the Gunnarites antarcticus Zone (Olivero, 198 1) to the Pachydiscus ultimus Zone, and is abundant in the highest ammonite-bearing horizon of Seymour Island.
Synonym list:
? 1890 Hamites elatior Forbes?. - White : p.13 fig. 1-2
? 1903 Hamites elatior Forbes?. - Weller : p.418 pl. 2; fig. 3
? 1903 Hamites sp. Weller. - Weller : p.418 pl. 2; fig. 4
1909 Anisoceras notabile Whiteaves. - Kilian & Reboul : p.15 pl. 2, fig. 1; pl. 2, fig. 4
1953 Diplomoceras lambi Spath. - Spath : p.17 pl. 2, fig. 1-3; pl. 3, fig. 1
1953 Diplomoceras lambi Spath. - Spath : p.17 pl. 2, fig. 1-3; pl. 3, fig. 1
1965 Diplomoceras sp. . - BIRKELUND : p.67 pl. 16; fig. 1-2
1966 Eudiplomoceras raggatti Brunnschweiler. - BRUNNSCHWEILER : p.18 fig. 7; text-fig. 4, 5, 6
1976 Diplomoceras lambi Spath. - Valle & Rinaldi : p. 6-9 pls. 1-10
1986 Diplomoceras lambi Spath. - MACELLARI : p. 15, 18, 19 fig. 11.13, 14.1, 15, 16
Was used in synonym list of:
Diplomoceras cylindraceum Defrance 1816
Stratigraphy - relative ages:
Maastrichtian: MACELLARI (1986)

White,C.A.. (1890):
On certain Mesozoic fossils from the island of St. Paul's and St. Peter's in the Straits of Magellan . Proc. U. S. natn. Mus. Vol. 13 p. 13-14

Weller,S.. (1903):
The Stokes collection of Antarctic fossils . J. Geol. Vol. 11 p. 413-419

Kilian,W.. and Reboul,P.. (1909):
Les cephalopodes neocretaces des lies Seymour et Snow Hili. . Wiss. Ergebn. schwed. Südpolarexped. Vol. 3(6) p. 1-75

Spath,L.F.. (1953):
The upper Cretaceous cephalopod fauna of Graham Land . Scientific Reports of the Falkland Islands Survey Department Vol. 3 p. 60

BIRKELUND,T.. (1965):
Ammonites from the Upper Cretaceous of West Greenland . Meddeleser om Gronland Vol. 179 p. 1-192

Upper Cretaceous ammonites from the Carnarvon Basin of Western Australia 1: the heteromorph Lytoceratina. . Bulletin of the Bureau of Mineral Resources, Geology and Geophysics Vol. 58 p. 5-58

Valle,D.R.A.. and Rinaldi,C.A.. (1976):
Sobre la presencia de Diplomoceras lambi Spath en la Isla Vicecomodoro Marambio . Inst. Antarct. Argent. Vol. 191 p. 40 pp.

MACELLARI,C.E.. (1986):
Late Campanian-Maastrichtian ammonite fauna from Seymour Island (Antarctic Peninsula) . Memoirs of the Paleontological Society Vol. 18(2) p. 1-55

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