After Hou & Bergström, 1997, Whittington, Chang, Dean, Fortey, Jell, Laurie, Palmer, Repina, Rushton & Shergold, 1997 and Gon III, 2002

<==o †Agnostida Salter, 1864 [nom. correct. Shergold, Laurie & Sun, 1990 pro Agnostini Salter, 1864; Miomera Jaekel, 1909; Agnostida Kobayashi, 1935
   `--o †Agnostina Salter, 1864 [nom. correct. Shergold, Laurie & Sun, 1990 pro Agnostini Salter, 1864]
      |?-o †Phalacromidae Hawle & Corda, 1847
      |  |--o †Phalacroma Hawle & Corda, 1847 [Platagnostus Howell, 1935b]
      |  |  |-- †P. bibullatus (Barrande, 1846) [Battus bibullatus Barrande, 1846]
      |  |  `-- †P. immensus (Howell, 1935b) [Platagnostus immensus Howell, 1935b]
      |  |--o ?†Dignagnostus Hajrullina in Repina, Petrunina & Hajrullina, 1975
      |  |  `-- †D. grandis Hajrullina in Repina, Petrunina & Hajrullina, 1975
      |  `--o †Lisogoragnostus Rozova in Lisogor, Rozov & Rozova, 1988
      |     `-- †L. kalisae Rozova in Lisogor, Rozov & Rozova, 1988
      |?-o †Sphaeragnostidae Kobayashi, 1939a
      |  `--o †Sphaeragnostus Howell & Resser in Cooper & Kindle, 1936
      |     `-- †S. similaris (Barrande, 1872)
      |--o †Condylopygoidea Raymond, 1913a
      |  `--o †Condylopygidae Raymond, 1913a
      |     |--o †Condylopyge Hawle & Corda, 1847 [Paragnostus Jaekel, 1909; Fallagnostus Howell, 1935b]
      |     |  |-- †C. rex (Barrande, 1846) [Battus rex Barrande, 1846; Paragnostus rex (Barrande) Jaekel, 1909]
      |     |  `-- †C. blayaci (Howell, 1935b) [Fallagnostus blayaci Howell, 1935b]
      |     `--o †Pleuroctenium Hawle & Corda, 1847 [Dichagnostus Jaekel, 1909]
      |        `-- †P. granulatum (Barrande, 1852) [Battus granulatus Barrande, 1852; Dichagnostus granulatus (Barrande) Jaekel, 1909]
      `--o †Agnostoidea M'Coy, 1849
         |-- †Agnostidae M'Coy, 1849 [Micragnostidae Howell, 1935; Glyptagnostidae Whitehouse, 1936; Rudagnostidae Lermontova, 1951]
         |-- †Ptychagnostidae Kobayashi, 1939 [synonyms]
         |--o †Spinagnostidae Howell, 1935 [Quadragnostidae Howell, 1935a sensu Öpik, 1979; Cyclopagnostidae Howell, 1937]
         |  |?-o †Pseudoperonopsis Harrington, 1938; M. Camb. WEu. NA. Aust. EAs.
         |  |  `-- †P. sallesi (Munier-Chalmas & Bergeron, in Bergeron, 1889) [Agnostus sallesi Munier-Chalmas & Bergeron, in Bergeron, 1889]
         |  |--o †Doryagostinae Shergold, Laurie & Sun, 1990
         |  |  |--o †Doryagnostus Kobayashi, 1939a [Ceratagnostus Whitehouse, 1939]; M. Camb. NA. Eu. CAs. EAs.
         |  |  |  `-- †D. incertus (Brögger, 1878) [Agnostus incertus Brögger, 1878]
         |  |  |  |-- †D. magister (Whitehouse, 1939) [Ceratagnostus magister Whitehouse, 1939]
         |  |  |  `-- †D. notalibrae
         |  |  |--o †Itagbostus Öpik, 1979; M. Camb. Aust. CAs. EAs. NA. CEu.
         |  |  |  `-- †I. elkedraensis (Etheridge, 1902) [Agnostus elkedraensis Etheridge, 1902]
         |  |  `--o †Rhodotypiscus Öpik, 1979; M. Camb. ENA. Aust. CAs.
         |  |     `-- †R. nasonis Öpik, 1979
         |  `-- †Spinagostinae Howell, 1935 [Spinagnostidae Howell, 1937; Cyclopagnostinae Howell, 1937; Hypagnostinae Ivshin, 1953; Euagnostinae Öpik, 1979]
         |-- †Paronopsidae Westergård, 1936
         |-- †Diplagnostidae Whitehouse, 1936 [incl. Pseudagnostidae]
         |--o †Clavagnostidae Howell, 1937
         |  |?-o †Utagnostus Robinson, 1964
         |  |  `-- †U. trispinulus Robinson, 1964
         |  |--o †Clavagnostus Howell, 1937 [Tomorhachis Resser, 1938; Culipagnostus Rusconi, 1952; Stigmagnostus C. Poulsen, 1960; Acanthagnostus Qian, 1982; Clavagnostus (Leptagnostus) Lu & Lin, 1989] [Clavagostinae Howell, 1937]
         |  |  |-- †C. repandus (Westergård, in Holm & Westergård, 1930) [Agnostus repandus Westergård, in Holm & Westergård, 1930]
         |  |  |-- †C. spinosa (Resser, 1938) [Tomorhachis spinosa Resser, 1938]
         |  |  |-- †C. chipiquensis (Rusconi, 1952) [Culipagnostus chipiquensis Rusconi, 1952]
         |  |  |-- †C. canotensis (Rusconi, 1951) [?Tomagnostus canotensis Rusconi, 1951; Stigmagnostus canotensis (Rusconi, 1951) C. Poulsen, 1960]
         |  |  |-- †C. longispinus (Qian, 1982) [Acanthagnostus longispinus Qian, 1982]
         |  |  `-- †C. lanceolatus Lu & Lin, 1989 [Clavagnostus (Leptagnostus) lanceolatus Lu & Lin, 1989]
         |  `--o †Aspidagnostinae Pokrovskaya, 1960
         |     |--o †Aspidagnostus Whitehouse, 1936 [Biragnostus Pokrovskaya, in Khalfin, 1960]
         |     |  |-- †A. parmatus Whitehouse, 1936
         |     |  `-- †A. elenae (Pokrovskaya, in Khalfin, 1960) [Biragnostus elenae Pokrovskaya, in Khalfin, 1960] [nomen nudum]
         |     `--o †Triadaspis Öpik, 1967
         |        `-- †T. bigeneris Öpik, 1967
         `-- †Metagnostidae Jaekel, 1909 [Arthrorhachidae Reymond, 1913a; Geragnostidae Howell, 1935b; Trinodidae Howell, 1935b]

Agnostida incertae sedis:

    †Agnostina:
            †Agnostogonus Öpik, 1967 [possibly a ptychagnostine or a spinagnostid]
                †A. incognitus Öpik, 1967
            †Archaeagnostus Kobayashi, 1939a
                †A. primigeneus Kobayashi, 1939a
            †Armagnostus Howell, 1937
                †A. megalaxis Howell, 1937
            †Blystagnostus Öpik, 1961b
                †B. laciniatus Öpik, 1961b
            †Ciceragnostus Kobayashi, 1937b
                †C. barlowi (Belt, 1868) [Agnostus barlowi Belt, 1868]
            †Delagnostus Öpik, 1961b
                †D. dilemma Öpik, 1961b
            †Gallagnostus Howell, 1935b
                †G. geminus Howell, 1935b
            †Glaberagnostus Romanenko, 1985
                †G. altaicus Romanenko, 1985
            †Grandagnostus Howell, 1935a
                †G. vermontensis Howell, 1935a
            †Hastagnostus Howell, 1937 [Hastagnostidae]
                †H. angustus Howell, 1937
            †Leiagnostus Jaekel, 1909 [Phoidagnostoides Pillet, in Capèra, Courtessole & Pillet, 1978]
                †L. erraticus Jaekel, 1909
                †L. migueli Sdzuy, 1958 [Phoidagnostoides migueli (Sdzuy) Pillet, in Capèra, Courtessole & Pillet, 1978]
            †Monaxagnostus Liu, 1982
                †M. yongshunensis Liu, 1982
            †Neoagnostus
                †N. denticulatus
            †Phalagnostus Howell, 1955 [Phalacromina Kobayashi, 1962]
                †P. nudus (Beyrich, 1845) [Battus nudus Beyrich, 1845]
                    †P. n. ovalis (Illing, 1916) [Phalacromina ovalis (Illing) Kobayashi, 1962]
            †Phaldagnostus Ivshin & Khalfin, 1960
                †P. orbiformis Ivshin & Khalfin, 1960
            †Phoidagnostus Whitehouse, 1936
                †P. limbatus Whitehouse, 1936
            †Plurinodus Öpik, 1967 [possibly a pseudagnostine]
                †P. discretus Öpik, 1967
            †Quadragnostus Howell, 1935a
                †Q. solus Howell, 1935a
            †Skryjagnostus Snajdr, 1957
                †S. pompeckji Snajdr, 1957
            †Toragnostus Robison, 1988
                †T. bituberculatus (Angelin, 1851) [Agnostus bituberculatus Angelin, 1851]
            †Valenagnostus Jago, 1976
                †V. marginata (Brögger, 1878) [Agnostus nudus Beyrich var. marginata Brögger, 1878]

Agnostina nomina nuda:

            †Cenagnostus Whittard, 1940
            †Clavagnostotes Lu & Lin, 1981
            †Kitatagnostus Ergaliev, 1965
            †Munagnostus Ivshin in Khalfin, 1960
            †Parapseudagnostus Petrunina, 1966
            †Pseudagnostella Koroleva, 1982

Note:

Agnostida sensu lato [Agnostina & Eodiscina] have usually been classified as primitive trilobites. Hou & Bergström (1997) clearly state that, in their opinion, Agnostida sensu lato as traditionally defined and treated in the latest edition of “Treatise“ is actually a polyphyletic taxon, Eodiscina being a group of primitive trilobites and Agnostina an anomalous group of early Crustacean-like arthropods.

Reference(s):