Imbrie, John.

American Museum of Natural History Scientific Publications

Ilikeican%MlsdllmoxfitatesPUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORYCENTRAL PARK WEST AT 79TH STREET, NEW YORK 24, N.Y.NUMBER 1754 DECEMBER 28, 1955New Species of Brachiopods"from theTraverse Group (Devonian) ofMichiganBY JOHN IMBRIE'INTRODUCTIONThe present paper describes two species of brachiopods from De-vonian rocks of the Michigan region, Pholidostrophia gracilis Imbrie,new species, and Strophodonta extenuata Imbrie, new species. Bothspecies are considered polytypic, hence the categories treated hereinclude six new subspecies: P. g. gracilis, P. g. nanus, S. e. extenuata,S. e. rockportensis, S. e. bellensis, and S. e. ferrenensis.The type material on which these species and subspecies are basedis housed at the United States National Museum. The holotype ofS. e. extenuata was collected from an abandoned shale pit of the AlpenaPortland Cement Company, SE 14 Sec. 18, T. 32 N., R. 9 E., AlpenaCounty, Michigan. Holotypes of all the other categories mentionedin this paper come from beds exposed in the quarry of the KellyIsland Lime and Transport Company, Rockport, Michigan.The writer is greatly indebted to Dr. G. Arthur Cooper, who madeavailable the extensive collections in his charge at the United StatesNational Museum and gave valuable taxonomic counsel.' Research Associate, the American Museum of Natural History, and AssociateProfessor of Geology, Columbia University.AMERICAN MUSEUM NOVITATES NDESCRIPTIONS OF SPECIES AND SUBSPECIESGENUS STROPHODONTA HALL, 1850Strophodonta extenuata Imbrie, new speciesFigures 1-20DISTINGUISHING CHARACTERS: Although this species exhibits anextraordinarily wide range of variation, several features combine todistinguish it without difficulty from known congeneric forms. Theoutline, although variable, is always markedly wider than long andgenerally subsemicircular. The lateral profile is always moderately tostrongly concavo-convex. Two extremes of ornamentation, with inter-mediate types, occur: some shells possess subequal and angular cos-tellae, numbering about 13 per 5 mm. at midlength, and decreasingregularly and gradually in size as they increase in number from beakto margin; other forms have costellae markedly coarser umbonallyand decreasing rapidly in size as they increase in number to about13 per 5 mm. near the front margin.DESCRIPTION: Shells of medium size. Outline variable, subsemicir-cular to transversely subelliptical; slightly mucronate. Slopes to cardi-nal extremities moderately concave; lateral profile moderately to deeplyconcavo-convex. Ornamentation varying between two extremes: someforms with costellae numbering about 13 per 5 mm. at midlength andincreasing in number gradually from beak to front margin as theydecrease in size; others with markedly larger umbonal costellae, de-creasing in size rapidly marginally. Costellae low, subround to sub-angular, about equal to striae in width.Pedicle valve: Lateral profile varying from moderately to stronglyconvex, generally evenly convex. Anterior profile generally evenly andeither moderately or strongly convex. Rarely subcarinate. Umbonalregion gently to moderately inflated. Interarea low. Interior withadductor scar from one-third to one-half of the length of the musclefield; extremities of ventral process narrowly divergent and projectingas tiny bosses.Brachial valve: Anterior profile commonly evenly and moderatelyconcave. Lateral profile either with greatest concavity between mid-length and the front margin, or evenly and moderately concave.Interior typical of the genus.OCCURRENCE: The species is known from the Bell, Rockport Quarry,Ferron Point, and Genshaw formations in Michigan, and from theArkona shale of Ontario.2 O. 1754IMBRIE: NEW BRACHIOPODSStrophodonta extenuata bellensis Imbrie,new species and subspeciesFigures 16-20DISTINGUISHING CHARACTERS: The following characteristics distin-guish this subspecies from conspecific groups: (1) small size; (2) sub-quadrate outline; (3) deeply concavo-convex lateral profile; (4) gentlyinflated umbonal region; (5) subgeniculate profile; (6) finely and ratheruniformly multicostellate ornamentation.DESCRIPTION: Shell small. Outline subquadrate, a little wider thanlong, slightly mucronate. Profile commonly strongly concavo-convex.Ornamentation uniformly and finely multicostellate; costellae low,rounded, subequal, numbering about 17 in a distance of 5 mm.Pedicle valve: Lateral profile moderately to strongly convex, withpoint of greatest convexity between midlength and front margin.Anterior profile evenly convex. Umbonal region gently inflated.Brachial valve: Lateral and anterior profiles gently and evenlyconcave. Umbonal region depressed.MEASUREMENTS OF HOLOTYPE: Length, 21 mm.; width, 24 mm.;thickness, 8 mm.OCCURRENCE: Bell shale of Michigan.HOLOTYPE: U.S.N.M. No. 124325 from the upper Bell shale.Strophodonta extenuata rockportensis Imbrie,new species and subspeciesFigures 6-10DISTINGUISHING CHARACTERS- This subspecies resembles S. extenu-ata extenuata in the character of its ornamentation, but differs in beinglarger and flatter. The ornamentation, large size, and relatively lowconvexity distinguish S. extenuata rockportensis from other conspecificgroups.DESCRIPTION: Shell large, commonly 30 mm. long. Outline trans-versely subelliptical. Lateral profile slightly or moderately convex.Ornamentation as in S. extenuata extenuata.Pedicle valve: Lateral and anterior profiles evenly convex. Umbonalregion commonly slightly swollen.Brachial valve: Lateral and anterior profiles gently and evenlyconcave.MEASUREMENTS OF HOLOTYPE: Length, 22 mm.; width, 26 mm.;thickness, 7 mm.1955 3AMERICAN MUSEUM NOVITATES31 2 45 6 7 810 11 1213 145IFIGS. 1-5. Holotype of Strophodontta extenutata ferronensis Il11brie. X 1.1. Brachial view. 2. Pedicle view. 3. Posterior view. 4. Anterior vXiew.5. Lateral view.FIGS. 6-10. Holotype of Strophlodonzta extenntata rockportensis Imbrie. X 1.6. Brachial view. 7. Pedicle viewx. 8. ILateral view. 9. Posterior viev. 10.Anterior viexx.FIGS. 11-15. Holotype of Strophodonta extenutata extenitata Imbric. X 1.11. Brachial view. 12. Pedicle view. 13. Posterior view. 14. Lateral view.15. Anterior view.4 NO. 1754IMBRIE: NEW BRACHIOPODS1916 17 18 2021 22 23 24 25FiC;s. 16-20. Holotype of Strophodonta extenuata bellensis Imbrie. X 1.16. Brachial viex. 17. Pedicle view. 18. Lateral view. 19. Posterior view.20. Anterior vieNr.FIGS. 21-23. Holotype of Pholidostrophia gracilis gracilis Imbrie. X 1.21. Brachial view. 22. Pedicle view. 23. Lateral view.FIGS. 24-25. Holotype of Pholidostrophia gracilis nanus Imbrie. X 2.24. Pedicle view. 25. Lateral view.OCCURRENCE: ILower 8 inches of the Rockport Quarry limestone ofMichigan.HOLOTYPE1: U.S.N.M. No. 124327 from the Rockport Quarry lime-stone.Strophodonta extenuata extenuata Imbrie,new species and subspeciesFigures 11-15DISTINGUISHING CHARACTERS: The following characters distinguishthis subspecies: (1) transversely subsemicircular outline; (2) moder-ately to strongly concavo-convex profile; (3) inflated umbo; (4) thecharacter of the ornamentation.DESCRIPTION: Shell of medium size. Outline transversely subsemi-circular. Lateral profile nmoderately to deeply concavo-convex. Orna-mentation multicostellate; costellae rounded and coarse umbonally,rapidly increasing in number and decreasing in size towards the margin,where the rib count is about 13 in a distance of 5 mm.; costetlaesubangular to subround, narrower than striae; striae rounded.Pedicle valve: Lateral profile moderately to strongly and evenly1955 5AMERICAN MUSEUM NOVITATESconvex. Anterior profile with greatest convexity along the midline,sloping with gentle convexity laterally. Umbonal region swollen.Brachial valve: Lateral profile moderately convex, shallower thanthe pedicle valve. Anterior profile with greatest concavity along themidline, corresponding to the low pedicle carina.MEASUREMENTS OF HOLOTYPE: Length. 25 mm.; width, 28 mm.;thickness, 8 mm.OCCURRENCE: Lower Ferron Point formation of Michigan; Arkonashale of Ontario.HOLOTYPE: U.S.N.M. No. 124326 from the lower Ferron Pointformation.Strophodonta extenuata ferronensis Imbrie,new species and subspeciesFigures 1-5DISTINGUISHING CHARACTERS: In ornamentation this subspecies re-sembles S. extenuata bellensis, but it may be distinguished by itslarger size and the even convexity of the pedicle valve. In shape itresembles specimens of S. extenuata rockportensis, but it differs inornamentation.DESCRIPTION: Of medium size. Outline transversely subelliptical tosubquadrate, width a little greater than length. Lateral profile mod-erately concavo-convex. Ornamentation commonly as in S. extenuatabellensis, rarely with coarser umbonal costellae.Pedicle valve: Lateral and anterior profiles evenly and gently tomoderately convex. Umbonal region gently inflated.Brachial valve: Lateral and anterior profiles evenly and gentlyconcave, shallower than pedicle valve. Umbonal region slightly de-pressed.MEASUREMENTS OF HOLOTYPE: Length, 26 mm.; width, 30 mm.;thickness, 8 mm.OCCURRENCE: Upper Ferron Point formation of Michigan; Arkonashale of Ontario.HOLOTYPE: U.S.N.M. No. 124333 from the upper Ferron Pointformation.GENUS PHOLIDOSTROPHIA HALL AND CLARKE, 1892Pholidostrophia gracilis Imbrie, new speciesFigures 21-25DISTINGUISHING CHARACTERS: The following characters distinguishthis species: (1) narrow outline, with lateral margins tapering con-6 NO. 1754IMBRIE: NEW BRACHIOPODStinuously anteriorly from the cardinal extremities; (2) very low andeven profile; (3) thin, closely appressed valves.DESCRIPTION: Size variable, commonly large. Outline transverselysubelliptical to subquadrate; length-width ratio high for the genus,about 0.85; hinge width the greatest width; cardinal extremities acute,lateral margins tapering continuously forward from the cardinal ex-tremities. Lateral profile gently and evenly concavo-convex.Pedicle valve: Lateral and anterior profiles very gently and evenlyconvex. Umbonal region slightly swollen. Interior with diductors ex-tending to or beyond the midpoint of the valve.Brachial valve: Lateral and anterior profiles greatly and evenlyconvex. Adductor field typical of the genus.OCCURRENCE: The species is known from the Bell, Rockport Quarry,Ferron Point, and Genshaw formations.Pholidostrophia gracilis gracilis Imbrie,new species and subspeciesFigures 21-23DESCRIPTION: Mean length about 16 mm., with a few individuals25 mm. long. Otherwise as described for the species.MEASUREMENTS OF HOLOTYPE: Length, 16 mm.; width, 19 mm.;thickness, 3.6 mm.OCCURRENCE: Lower Bell shale, Rockport Quarry limestone, FerronPoint formation, and Genshaw formation.HOLOTYPE: U.S.N.M. No. 124318 from the Rockport Quarry lime-stone.Pholidostrophia gracilis nanus Imbrie,new species and subspeciesFigures 24-25DESCRIPTION: Mean length about 11 mm., with largest individualabout 13 mm. long. Otherwise as described for the species.MEASUREMENTS OF HOLOTYPE: Length, 10.3 mm.; width, 12.8 mm.;thickness, 2.0 mm.OCCURRENCE: Upper 12 feet of Bell shale.HOLOTYPE: U.S.N.M. No. 124320 from the upper Bell shale.1955 7

New brachiopods

Abstract

Similar works

Full text

Available Versions

American Museum of Natural History Scientific Publications