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Acmarhachis
Classification
Phylum:
Unknown
Class:
Trilobata
Order:
Agnostida
Superfamily:
Agnostoidea
Family:
Agnostidae
Formal Genus Name and Reference:
Acmarhachis RESSER, 1938, p. 47
Type Species:
* A. typicalis, OD, holotype (RESSER, 1938, pl. 10, fig. 5), 94858, USNM, Washington, D.C.
Images
(Click to enlarge in a new window)
Fig. 222,4a–c. *A. typicalis; a, Upper Cambrian (Dresbachian), USA (McCalla, Alabama), holotype, pygidium, USNM 94858, × 10 (new); b,c, Upper Cambrian (Dresbachian, Crepicephalus Zone), USA (McGill, Nevada), b, cephalon, USNM 143145a and c, pygidium, USNM 143145b, × 10 (Palmer, 1962a, pl. 2, fig. 12–13).
Synonyms
Cyclagnostus
Geographic Distribution
USA (Alaska, Alabama, Nevada, Maryland, Vermont), Crepicephalus to Dunderbergia Zones; Canada (British Columbia, Northwest Territories), Cedaria minor-C. brevifrons Zones; Australia (Queensland), D. torosa or A. janitrix to W. iota or R. apsis Zones, (Tasmania), post-Idamean; Kazakhstan, Kormagnostus simplex Zone; Russia (Kharaulakh), L. laevigata to P. pseudangustilobus Zones; China (Zhejiang), L. sinensis Zone, (Anhui), zone uncertain.
Age Range
Beginning Stage in Treatise Usage:
Upper Cambrian
Beginning International Stage:
Guzhangian
Fraction Up In Beginning Stage:
0
Beginning Date:
498.75
Ending Stage in Treatise Usage:
Upper Cambrian
Ending International Stage:
Cambrian Stage 10
Fraction Up In Ending Stage:
0
Ending Date:
486.85
Description
Median preglabellar furrow weak or absent, Glabella with long ogival to subquadrate anterior lobe, F3 straight, posterior lobe with forwardly directed F2 furrows, occasionally joining to form chevronate furrow, glabellar node located from well behind F2 furrows to near apex of chevronate furrow, basal lobes of moderate to large size, triangular, Pygidium with agnostoid articulating device, axiolobate, strongly constricted across M2, broad, tumid posterior lobe bearing terminal node and sometimes intranotular axis
References
Resser, C. E., \& B. F. Howell. 1938. Lower Cambrian Olenellus Zone of the Appalachians. Geological Society of America, Bulletin 49:195-248, 13 pl .
Museum or Author Information
Classification
Phylum:
Unknown
Class:
Trilobata
Order:
Agnostida
Superfamily:
Agnostoidea
Family:
Agnostidae
Formal Genus Name and Reference:
Acmarhachis RESSER, 1938, p. 47
Type Species:
* A. typicalis, OD, holotype (RESSER, 1938, pl. 10, fig. 5), 94858, USNM, Washington, D.C.
Images
(Click to enlarge in a new window)
Fig. 222,4a–c. *A. typicalis; a, Upper Cambrian (Dresbachian), USA (McCalla, Alabama), holotype, pygidium, USNM 94858, × 10 (new); b,c, Upper Cambrian (Dresbachian, Crepicephalus Zone), USA (McGill, Nevada), b, cephalon, USNM 143145a and c, pygidium, USNM 143145b, × 10 (Palmer, 1962a, pl. 2, fig. 12–13).
Synonyms
Cyclagnostus
Geographic Distribution
USA (Alaska, Alabama, Nevada, Maryland, Vermont), Crepicephalus to Dunderbergia Zones; Canada (British Columbia, Northwest Territories), Cedaria minor-C. brevifrons Zones; Australia (Queensland), D. torosa or A. janitrix to W. iota or R. apsis Zones, (Tasmania), post-Idamean; Kazakhstan, Kormagnostus simplex Zone; Russia (Kharaulakh), L. laevigata to P. pseudangustilobus Zones; China (Zhejiang), L. sinensis Zone, (Anhui), zone uncertain.
Age Range
Beginning Stage in Treatise Usage:
Upper Cambrian
Beginning International Stage:
Guzhangian
Fraction Up In Beginning Stage:
0
Beginning Date:
498.75
Ending Stage in Treatise Usage:
Upper Cambrian
Ending International Stage:
Cambrian Stage 10
Fraction Up In Ending Stage:
0
Ending Date:
486.85
Description
Median preglabellar furrow weak or absent, Glabella with long ogival to subquadrate anterior lobe, F3 straight, posterior lobe with forwardly directed F2 furrows, occasionally joining to form chevronate furrow, glabellar node located from well behind F2 furrows to near apex of chevronate furrow, basal lobes of moderate to large size, triangular, Pygidium with agnostoid articulating device, axiolobate, strongly constricted across M2, broad, tumid posterior lobe bearing terminal node and sometimes intranotular axis
References
Resser, C. E., \& B. F. Howell. 1938. Lower Cambrian Olenellus Zone of the Appalachians. Geological Society of America, Bulletin 49:195-248, 13 pl .