CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY T THE UNIVERSITY OF MICHIGAN VOL. XVII, No. 3, pp. 77-121 (2 pls., 6 figs.) OC~OBER20, 1961 A NEW SPECIES OF BILLINGSITES, AN ASCOCERATID CEPHALOPOD, FROM THE UPPER ORDOVICIAN OGONTZ FORMATION OF MICHIGAN BY ROBERT V. KESLING MUSEUM OF PALEONTOLOGY THE UNIVERSITY OF MICHIGAN ANN ARBOR CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY Director: LEWIS B. KELLUM The series of contributions from the Museum of Paleontology is a medium for the publication of papers based chiefly upon the collection in the Museum. When the number of pages issued is sufficient to make a volume, a title page and a table of contents will be sent to libraries on the mailing list, and to individuals upon request. A list of the separate papers may also be obtained. Correspondence should be directed to the Museum of Paleontology, The University of Michigan, Ann Arbor, Michigan. VOLS.11-XV. Parts of volumes may be obtained if available. VOLUMEXVI 1. Two Late Pleistocene Faunas from Southwestern Kansas, by Claude W. Hibbard and Dwight W. Taylor. Pages 1-223, with 16 plates. 2. North American Genera of the Devonian Rugose Coral Family Digonophylli- dae, by Erwin C. Stumm. Pages 225-243, with 6 plates. 3. Notes on Jaekelocystis hartleyi and Pseudocrinites gordoni, two Rhombif- eran Cystoids Described by Charles Schuchert in 1903, by Robert V. Kesling. Pages 245-273, with 8 plates. 4. Corals of the Traverse Group of Michigan, Part VI, Cladopora, Striatopora, and Thamnopora, by Erwin C. Stumm. Pages 275-285, with 2 plates. 5. A Study of the Middle Devonian Widder Formation of Southwestern On- tario, by Jean D. Wright and Edward P. Wright. Pages 287-300, with 1 plate. VOLUMEXVII 1. Evaluation of Przibram's Law for Ostracods by Use of the Zeuthen Car- tesian-diver Weighing Technique, by Robert V. Kesling and Robert S. Takagi. Pages 1-58, with 5 plates. 2. A New Glyptocystites from Middle Ordovician Strata of Michigan, by Robert V. Kesling. Pages 59-76, with 3 plates. 3. A New Species of Billingsites, an Ascoceratid Cephalopod, from the Upper Ordovician Ogontz Formation of Michigan, by Robert V. Kesling. Pages 77-121, with 2 plates. VOL. XVII, NO.3, pp. 77-121 (2 pls., 6 figs.) OCTOBER 20, 1961 A NEW SPECIES OF BILLINGSITES, AN ASCOCERATID CEPHALOPOD, FROM THE UPPER ORDOVICIAN OGONTZ FORMATION OF MICHIGAN BY ROBERT V. KESLING CONTENTS Introduction . Locality . Previous references to Michigan specimens . Terminology of ascoceratid cephalopods . Systematic description . Order Ascoceratida . Family Ascoceratidae . Genus Billingsites Hyatt . Cephalopod buoyancy . Living Nautilus . General considerations . Billingsites' mode of life . Previous work on ascoceratids . Stages of development . .. Function of truncation . Potential buoyancies . Probable ontogenetic sequence . Literature cited . Plates . (after) INTRODUCTION NIGMATICALLY, the cephalopods on which this paper is based have been E known in publication for thirty-five years but they are new. Because the previous references were nomina nuda, the species has remained tech- nically undescribed and scientifically unknown. These fossils belong to a curious group of nautiloids, the Ascoceratida, which overcame the handicap of an unwieldy conch by truncation, casting off the earlier, impeding stages of the shell to adapt to a new mode of life. Although it has long been sus- pected that the Ordovician representatives, like their Silurian descendants, formed a cyrtoconic phragmocone in their youthful stages, each specimen previously described has consisted of only the expanded adoral part of the c conch, the segment retained by the animal after the final truncation. One ROBERT V. KESLING of the specimens described here is the first Ordovician ascoceratidan dis- covered which kept a part of the cyrtoconic phragmocone. Because the terminology of these cephalopods is not only rather ex- tensive but also varies from author to author, there is a section to explain the terms that I use. In the systematic descriptions, the nature of the cephalopods and their classification is discussed under the order, family, and genus for the purpose of showing the position of the new species. Treat- ment of the genus Billingsites includes a key to the well-substantiated spe- cies now assigned to it. Longitudinal sections of selected specimens of the new species reveal significant details of the internal organization. A few specimens show ven- tral markings which appear to represent aponeurotic bands in the adult living chamber. From information available, it is possible to reconstruct the cephalopod with some degree of assurance. The paper closes with certain inferences and hypotheses regarding the animal's mode of life, particularly with reference to the changes of buoyancy engendered by truncation. As might have been expected, the first published mention of the occur- rence of Billingsites in Michigan was by August F. Foerste, the leading authority of his day on cephalopods, who did outstanding work on the Ascoceratidae in America. As Dr. George M. Ehlers informs me, Dr. Foerste willingly gave of his time to anyone with a problem involving cephalopods and helped with the identification of many specimens in the Museum of Paleontology of the University of Michigan. Still, today, in looking through the drawers of Paleozoic fossils, one occasionally comes across specimens accompanied by the notation "Send to Foerste"-nostalgic reminders of the generosity of a great paleontologist and the high regard in which he was held by his contemporaries. Yet it was also characteristic of Dr. Foerste that he could be persuaded to accept responsibility for more species than he could possibly describe, even at his tremendous tempo of investigation and volume of publication. For one of the fossils described here, UMMP No. 983 1, the Museum of Paleontology has a catalogue card stating that this specimen was to be the holotype of a species to be described by Dr. Foerste under the name "Bill- ingsites newberryi noquettensis." Further, R. C. Hussey in 1926 and 1950 used this name in faunal lists and illustrated the specimen in 1926. From 1924, when he first acknowledged the existence of the species, until his death in 1936, Dr. Foerste evidently did not get around to describing the Michigan Billingsites. It seems fitting, as a tribute to his yeoman work on Billingsites and his recognition of the Michigan cephalopod as new, to use Dr. Foerste's suggested name "noquettensis" and to utilize his intended holotype as the actual holotype of the new species. A NEW SPECIES OF BILLINGSITES 79 I gratefully acknowledge the kind suggestions by Dr. George M. Ehlers and the critical review of the manuscript by Dr. Lewis B. Kellum and Dr. Chester A. Arnold. Specimens are catalogued and deposited in the Museum of Paleontology of the University of Michigan. LOCALITY All specimens are from the same locality and were collected by R. C. Hussey prior to the publication of his paper in the Contributions from the Museum of Geology, Vol. 2, in 1926. Only one specimen, UMMP No. 983 1, which was illustrated by Hussey in 1926 (PI. 8, Figs. 10-12), was cata- logued before 1961. The other specimens had been retained in the general collection, accompanied by data on the occurrence and collector. Field in NWg sec. 25, T. 39 N., R. 21 W., east of the Swedish Church and about % mile south of the home of J. B. Stratton (located in SWS sec. 24 of same twp.), west side of Stonington Peninsula, Delta Co., Michigan. Locality 8 of Hussey (1926, pp. 116-17, 139). Upper Ordovician Richmond group, Ogontz formation (Ogontz member of the Stonington beds in Hussey's classification). PREVIOUS REFERENCES TO MICHIGAN SPECIMENS As pointed out in the introduction, A. I?. Foerste was the first to refer to these cephalopods. He wrote (1924, p. 222) : "Specimens [of Billing- sites] occur also in the Richmond of Bay de Noc peninsula, east of Escana- ba, Michigan." Two years later, R. C. Hussey (1926, p. 182), placed the name "Billing- sites newberryi noquettensis" in faunal lists of the Ogontz formation, and illustrated (PI. 8, Figs. 10-12) one specimen, UMMP No. 9831. Subsequently, Foerste made three references to the occurrence: 19283 (p. 223), "Billingsites is known . in the Ogontz division of the Stonington member east of Escanaba in northern Michigan . ."; 1929a (p. 40), "Bill- ingsites occurs in the Richmond of Anticosti, Michigan, Indiana, Ohio, and in the Maquoketa phase of the Richmond in eastern Iowa"; and 1929b (p. 157), "Billingsites is widely distributed on the American continent, occurring . on the peninsula east of Escanaba in northern Michigan, . ." Miller (19326, p. 27), in his revision of the group, stated: "Also, Foerste has mentioned in his recent publications that unnamed representa- tives of 'Billingsites' occur in . the Ogonotz [sic] division of the Stoning- ton (Richmond) of the peninsula east of Escanaba in northern Michigan. Part of these forms doubtlessly represent Billingsites s.s. and part the genus described below as Schuchertoceras, but the published information in regard to them is not sufficient to allot them." 80 ROBERT V. KESLING In 1950 (p. 20) Hussey again listed "Billingsites newberryi noquetten- sis Foerste" from the Ogontz formation. In 1952 (p. 51) he without doubt had this species in mind when he included "Billingsites newberryi (Bill- ings) " in his faunal list of the Ogontz formation. The specimens unquestionably belong to the genus Billingsites as re- stricted by Miller in 1932. The species newberryi, however, was quite prop- erly assigned to his new genus Schuchertoceras by Miller (19323, p. 31). Hence, "noquettensis" must be used as a specific rather than a subspecific name, and the designation of "Billingsites newberryi" by Hussey in 1952 is entirely erroneous. TERMINOLOGY OF ASCOCERATID CEPHALOPODS Only the terms which have special meaning as used for ascoceratid ceph- alopods need be discussed. An extensive glossary of cephalopod terms is offered by Flower (1946, pp.