More Mississippian belemnites

New Mississippian belemnites comprise 3 new genera, containing 5 named and one unnamed new species. Eobelemnites? sp. is from the rocks of Chester age of Alabama. Other species are based upon 8 specimens from the Fayetteville shale of Arkansas and more than 250 specimens from the Chainman shale of Utah. The new morphologic terms septal line and neck lobe are proposed. Some of the new forms have phragmocones which are very close to those of true and supposed bactritids, raising the question as to whether some such supposed bactritids may be based upon exfoliated belemnoid phragmocones. Review of features of the Aulococeratidae indicates that its distinction from the Belemnitidae is not warranted. Details of morphology are discussed, not all of which are explained satisfactorily from the present material, notably, variation of the rostral tips, vesicular structure in the rostrum, thinness of conotheca and absence of a clear protoconch suggesting resorption of protoconch and early phragmocone within the rostrum. Both Belemnitidae and Belemnoteuthidae occur in Permian and Triassic; Mississippian forms are Belemnitidae, but show some diversity of form and structure suggesting an appreciably older derivation of the Coleoidea.

This record provided courtesy of AGI/GeoRef.

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