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Memoir 10

Part 1: Revision of Buttsoceras
Part 2: Notes on the Michelinoceratida

By R. H. Flower, 1962, 58 pp., 6 plates, 1 index.

New material of Buttsoceras increases its range from Alabama through southern New Mexico and into northern Utah; it appears confined to the very latest phase of the Cassinian. The genus possesses a nonsegmental lining in the siphuncle, thickening gently apicad-like very slender endocones, which may terminate in a narrow tube that may be traversed by diaphragms. The inadequately known Oxfordoceras is not distinguishable from Buttsoceras; uncertainty surrounds the origin of its genotype. Buttsoceras shows fine lamellae in the lining of the siphuncle and thin homogeneous rings; it is referred to the Troedssonellidae of the Michelinoceratida. The study also involved some material referred to Michelinoceras, present with Buttsoceras in the Odenville and possibly in the Garden City Formation; M. primum, form the lower Cassinian part of the El Paso, is the oldest representative of the order Michelinoceratida so far recognized. The family Troedssonellidae is revised to include Buttsoceras.

This study is a reinvestigation of Buttsoceras, involving new and some old material. The genus was first distinguished as an orthocone generalized in most features, being a straight slender shell with transverse sutures and a subcentral tubular siphuncle, but set apart by the presence of a free tube within the siphuncle. This was, however, only one of several morphological surprises yielded by the study of the older cephalopods. The new material which forms the basis of the present study shows the supposed free tube, which is perfectly visible and obvious in the suite of type specimens of Buttsoceras adamsi, to result from a peculiar preservation phenomenon. Buttsoceras actually develops within its siphuncle a lining, thickening gently apicad; under slight silicification, shell wall, septa, the exterior of the siphuncle, and the inner surface of the lining are replaced, but the main mass of the lining remains calcareous. Under leaching, such specimens present the aspect of a free tube within the siphuncle. The condition is analogous to that noted by Yochelson in Palliseria, in which the thick shell wall, being silicified on the outer and inner surfaces, presents the deceptive aspect of being composed of three original layers. It should be noted that the previous known material of Buttsoceras consisted exclusively of a suite of silicified specimens picked up on deeply leached outcrops of the Odenville Limestone.

The condition is shown strikingly by the specimen here described as the holotype of Buttsoceras williamsi, from the upper cherty beds of the Garden City Formation. It demonstrates the nature of the lining of Buttsoceras in a specimen very similar in general proportions to Buttsoceras adamsi itself, but though the specimen was partly silicified, showing silicification of the inner surface of the lining, it was found unleached in limestone.

The order Michelinoceratida is discussed, tracing the main evolution as previously known, making some new contributions, and pointing out problems which still remain. Previously proposed family names are summarized, with some indication of their value and scope. A following section describes the families Proteoceratidae, describing the genera briefly and including some new ones; the new families Sphooceratidae, Engorthoceratidae, Offleyoceratidae are proposed, with new genera in some instances. A final section deals with contributions to the morphology of Orthoceros regularis, Pleurorthoceras clarkesvillense, and P. selkirkense, and Dawsonoceras. The previous paper (Part I), in dealing with the revision of Buttsoceras, and necessarily extended to include some Michelinoceras associated with and in part formerly confused with that genus, led to the recognition and revision of the Troedssonellidae and consequent restriction of the Michelinoceratidae.

This associated work (Part II) further continues the stirring of the troubled waters of the Michelinocertida, one of the largest and at the same time certainly the most poorly known of the orders of the Nautiloidea. Even though the results may be best summarized by the line from a Pick and Hammer Club song, "I've organized my ignorance," it may be that the present imperfect results will serve toward clarification of the problem of understanding the morphology, evolution, and classification of this great group. Some years back the writer had been undertaking investigation of this group; a part of this work, an analysis of the forms of the Bohemian Basin, was necessarily interrupted because of a move to an institution where Barrande's work was not available. This matter has been corrected recently, but completion of the investigation has not yet been possible. However, it has seemed relevant to add to the preceding work such observations as were ready for publication. They include (1) a discussion of the order Michelinoceratida and the family Michelinoceratidae, (2) a summary of families previously proposed now known to belong to the Michelinoceratida, (3) proposal of some new families and genera, already long delayed, and (4) description and illustration of some crucial forms of unusual morphological interest, a disparate lot to be sure, but including further investigation of the morphology of Orthoceros regularis, investigation of the remarkable Cycloceras selkirkense, which proves to show a Cycloceras-like surface only when cameral deposits are exfoliated from the internal mold. This with the allied Orthoceras clarkesvillense combine to form a distinctive new genus, Pleurorthoceras. Illustration and brief description of the familiar Dawsonoceras follow, which shows rather similar cameral deposits, but exhibits annuli of the aspect of the Michelinoceratidae in a siphuncle which has recumbent septal necks restricting otherwise tubular siphuncle segments at the septal foramina, a feature previously unreported.

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