Gastrioceras

Gastrioceras specimen, photographed by Linda Spashett.

Belongs within: Ammonoidea.

Gastrioceras is an Lower to Middle Pennsylvanian (Upper Carboniferous) genus of ammonoid.

Characters (from Gordon 1964): Conch subglobose to subdiscoidal at maturity, more or less barrel-shaped in immaturity, planorbital when young. Venter well-rounded; umbilicus moderately involute to evolute; umbilical shoulder ornamented by generally transversely elongate nodes. Transverse sculpture may or may not include strong ribs or sinuous lirae; longitudinal lirae present in some species confined to nodes or generally over ventral region and flanks. Suture with eight lobes and saddles; ventral lobe deeply divided into two narrow asymmetrical prongs, first lateral lobe fairly symmetrical, long and pointed.

<==Gastrioceras
    |  i. s.: G. angulatum Girty 1911 P68
    |         G. caneyanum Girty 1909 P68
    |         G. excelsum P68
    |         G. globulosum P68
    |         G. hyattianum Girty 1911 P68
    |         G. richardsonianum Girty 1909 P68
    |         G. serratum Girty 1908 P68
    |         G. simulator Girty 1910 P68
    |         G. venatum Girty 1911 P68
    |         G. welleri P68
    |--G. (Branneroceras) P68
    |    |--G. (B.) branneri Smith 1896 P68
    |    |--G. (B.) henbesti Gordon 1964 P68
    |    `--G. (B.) textum Gordon 1964 P68
    `--G. (Lissogastrioceras) P68
         |--G. (L.) adaense P68
         `--G. (L.) fittsi P68

*Type species of generic name indicated

REFERENCES

Gordon, M., Jr. 1964. Carboniferous cephalopods of Arkansas. Geological Survey Professional Paper 460.

[P68] Purnell, L. R. 1968. Catalog of the Type Specimens of Invertebrate Fossils. Part I: Paleozoic Cephalopoda. United States National Museum Bulletin 262: 1-198.