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Species Nostoceras (Nostoceras) colubriformis Stephenson 1941

[1] pl. 4, figs. 1-4 Ifrim et al. (2004) [2] text-fig. 14c Ifrim et al. (2004)

Alternative name:
Nostoceras colubriformis Stephenson 1941
Diagnosis / Definition:
Ifrim et al. (2004):
Description: Tests are evolute and highly trochospiral with a low expansion rate. Apical angle of 20 degrees in early juveniles increases to 35 degrees from the third whorl onwards. An initial whorl (diameter of c. 3 mm) is uncoiled at an angle of c. 40° from the succeeding trochospiral whorl. Juvenile whorl section is rounded to slightly subreetangular with WH/WB c. 1·1. Whorl sections are flattened at the contact between whorls. The outer surface of a whorl is covered by c. 40 prorsiradiate simple and forked ribs, and three to four constrictions per whorl. Bifurcation originates in weak bullae located on the outer whorl suture. A second row of elongated tubercles is present on the inner whorl suture. These rows are absent on the initial whorl but present on all succeeding ones. The number of rib bifurcations increases with whorl diameter. Tubercles described for Nostoceras (Nostoceras) colubriformis by Kennedy and Cobban (1993c) cannot be seen on the Cerralvo specimens, probably because of bad preservation of the test. No final hook is preserved. The suture line is simple and similar to that of other species of Nostoceras.
Discussion / Comments:
Ifrim et al. (2004):
Remarks: The ribs are less sharp than described by Stephenson (1941) but with typical patterns for the species. The absence of faint tubercles described by Stephenson may be an artefact and result of abrasion. The species differs from Nostoceras (Nostoceras) alternatum described herein by having a more rounded whorl section and less prominent ornament. The initial whorl differs from that of N. (N.) rugosum in having a closed umbilicus and a different angle of uncoiling. Occurrence: Nostoceras (Nostoceras) colubriformis has been described from the Upper Campanian Saratoga Chalk of Arkansas (Kennedy and Cobban 1993b) and the Nacatotch Sand of the Maastrichtian Navarro Formation of Texas (Stephenson 1941).

 Ordo Ammonoidea
  Subordo Ancyloceratina
   Superfamilia Turrilitaceae
    Familia Nostoceratidae
     Genus Nostoceras
      Subgenus Nostoceras (Nostoceras)
       Species Nostoceras (Nostoceras) colubriformis
Synonym list:
Ifrim et al. (2004):
1941 Nostoceras colubriformis Stephenson. - Stephenson : p.412 pl. 8, figs. 1-3
1993 Nostoceras (Nostoceras) colubriformis Stephenson. - Kennedy & Cobban : p.421 text-figs. 7.1-4, 7.8-9
2004 Nostoceras (Nostoceras) colubriformis Stephenson. - Ifrim et al. : 39, 35 pl. 4, figs. 1-4; text-fig. 14c
Stratigraphy - relative ages:
Maastrichtian - upper Campanian: Ifrim et al. (2004)

Stephenson,L.W.. (1941):
The larger invertebrates of the Navarro Group of Texas (exclusive of corals and crustaceans and exclusive of the fauna of the Escondido Formation) . University of Texas, Bulletin Vol. 4101 p. 641 pp

Kennedy,W.J.. and Cobban,W.A.. (1993):
Ammonites from the Saratoga Chalk (Upper Cretaceous), Arkansas . Journal of Paleontology Vol. 67(3) p. 404–434

Ifrim,C..; Stinnesbeck,W.. and López-Oliva,J.G.. (2004):
Maastrichtian cephalopods from Cerralvo, north-eastern Mexico . Palaeontology Vol. 47(6) p. 1575–1627

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