In synonymy:
Janus C. L. Koch, 1846 = Synemosyna Hentz, 1846 (Peckham & Peckham, 1888: 93, by S of the type species)
Simonella G. W. Peckham & E. G. Peckham, 1885 = Synemosyna Hentz, 1846 (Galiano, 1966a: 341)

type Synemosyna formica Hentz, 1846; gender feminine

N.B.: considered a senior synonym of Janus C. L. Koch, 1846: vol. 13: 21 [urn:lsid:nmbe.ch:spidergen:05337] (type J. gibberosus C. L. Koch, 1846 = Synemosyna formica Hentz, 1846 by Peckham & Peckham, 1888: 93 and of Simonella G. W. Peckham & E. G. Peckham, 1885a: 23 [urn:lsid:nmbe.ch:spidergen:04167] (type S. americana G. W. Peckham & E. G. Peckham, 1885) by Galiano, 1966a: 341.

Transferred to other genera:
Synemosyna atrogaster (Mello-Leitão, 1941) -- see Sympolymnia
Synemosyna edwardsi Cutler, 1985 -- see Sympolymnia
Synemosyna ephippiata Hentz, 1846 -- see Peckhamia
Synemosyna formosana (Saito, 1933) -- see Myrmarachne
Synemosyna lauretta G. W. Peckham & E. G. Peckham, 1892 -- see Sympolymnia
Synemosyna lucasi (Taczanowski, 1871) -- see Sympolymnia
Synemosyna melanura Mello-Leitão, 1917 -- see Sympolymnia
Synemosyna procera Thorell, 1877 -- see Toxeus
Synemosyna pumilio Karsch, 1880 -- see Myrmarachne
Synemosyna transversa Mukerjee, 1930 -- see Myrmarachne

In synonymy:
Synemosyna bicolor (G. W. Peckham & E. G. Peckham, 1892) = Synemosyna americana (G. W. Peckham & E. G. Peckham, 1885) (Cutler, 1981a: 343).
Synemosyna claustrorum (Mello-Leitão, 1933) = Synemosyna aurantiaca (Mello-Leitão, 1917) (Galiano, 1966a: 348).
Synemosyna gibberosa (C. L. Koch, 1846, T from Janus) = Synemosyna formica Hentz, 1846 (Peckham & Peckham, 1888: 93).
Synemosyna mastigostyla (Mello-Leitão, 1917) = Synemosyna aurantiaca (Mello-Leitão, 1917) (Galiano, 1966a: 348).
Synemosyna peckhami (Mello-Leitão, 1933) = Synemosyna myrmeciaeformis (Taczanowski, 1871) (Galiano, 1966a: 367).
Synemosyna simplex (Chamberlin, 1925) = Synemosyna decipiens (O. Pickard-Cambridge, 1896) (Galiano, 1966a: 355).
Synemosyna ypsilon (Piza, 1937) = Synemosyna aurantiaca (Mello-Leitão, 1917) (Galiano, 1966a: 349).

Nomina dubia:
Synemosyna bimaculata (Mello-Leitão, 1917c: 139, 1933a: 58, pl. 1, f. 3, f, Brazil, originally in Simonella) -- Galiano, 1966a: 354.
Synemosyna fasciata Mello-Leitão, 1922a: 222 (f, Brazil) -- Galiano, 1966a: 357.
Synemosyna fissidentata (Szombathy, 1913: 34, 57, f. 10-11, f, Paraguay, originally in Simonella) -- Galiano, 1966a: 357.
Synemosyna lunata (Walckenaer, 1837: 387, m, USA, originally in Myrmecium) -- Galiano, 1966a: 360.
Synemosyna magniscuti Mello-Leitão, 1939h: 292, f. 13-14 (m, Brazil) -- Galiano, 1966a: 367.
Synemosyna rubra (Walckenaer, 1837: 387, mf, USA, originally in Myrmecium) -- Galiano, 1966a: 360.
Synemosyna subtilis (Taczanowski, 1871: 122, f, Guyana, originally in Janus) -- Galiano, 1966a: 376.

Simonella americana Peckham & Peckham, 1885a: 24, pl. 1, f. 1 (Dm).
Simonella americana Peckham & Peckham, 1886: 341.
Simonella americana Peckham, Peckham & Wheeler, 1889: 252, pl. 12, f. 4 (m).
Simonella americana Peckham & Peckham, 1892: 80, pl. 7, f. 3 (m).
Simonella bicolor Peckham & Peckham, 1892: 83, pl. 7, f. 5 (Df) [urn:lsid:nmbe.ch:spidersp:055589].
Simonella americana F. O. Pickard-Cambridge, 1900: 170, pl. 11, f. 17 (m, Df).
Simonella bicolor F. O. Pickard-Cambridge, 1900: 171, pl. 12, f. 1-2 (f, Dm).
Synemosyna americana Galiano, 1966a: 345, f. 5-7, 33-35 (m).
Synemosyna bicolor Galiano, 1966a: 353, f. 13-14, 52-53, 63 (f).
Synemosyna americana Cutler, 1981a: 343 (S of Synemosyna bicolor).
Synemosyna americana Cutler, 1985: 89, f. 3.

Synemosyna ankeli Cutler & Müller, 1991: 172, f. 1-8 (Dmf).

Synemosyna aschnae Makhan, 2006c: 12, f. 1-7 (Df).

Simonella aurantiaca Mello-Leitão, 1917c: 138 (Df).
Simonella mastigostyla Mello-Leitão, 1917c: 140, f. 2 (Dm) [urn:lsid:nmbe.ch:spidersp:055591].
Simonella aurantiaca Mello-Leitão, 1933a: 58, pl. 1, f. 2 (f).
Simonella mastigostyla Mello-Leitão, 1933a: 59, pl. 1, f. 4, pl. 2, f. 8 (m, Df).
Simonella claustrorum Mello-Leitão, 1933a: 62, pl. 1, f. 6 (Df) [urn:lsid:nmbe.ch:spidersp:055590].
Simonella ypsilon Piza, 1937a: 311, pl. 1, f. 3-4, pl. 2, f. 5 (Dmf) [urn:lsid:nmbe.ch:spidersp:055594].
Synemosyna aurantiaca Galiano, 1966a: 348, f. 8-11, 44-46, 49, 61 (mf, T from Simonella, S of Simonella claustrorum, S. mastigostyla and S. ypsilon).
Synemosyna aurantiaca Cutler & Müller, 1991: 174, f. 13-15 (f; likely refers to another species per Perger, Rubio & Haddad, 2021: 73).

Simonella decipiens O. Pickard-Cambridge, 1896a: 163, pl. 19, f. 15-16 (Dmf).
Simonella decipiens F. O. Pickard-Cambridge, 1900: 171, pl. 12, f. 3-4 (mf).
Simonella simplex Chamberlin, 1925d: 232 (Df) [urn:lsid:nmbe.ch:spidersp:055593].
Synemosyna decipiens Galiano, 1966a: 355, f. 25-26, 55, 57 (f, S of Simonella simplex).
Synemosyna decipiens Cutler, 1985: 85, f. 4-12 (Dm).

Synemosyna formica Hentz, 1846: 368, pl. 22, f. 18 (Df).
Janus gibberosus C. L. Koch, 1846: vol. 13: 21, f. 1091 (Df) [urn:lsid:nmbe.ch:spidersp:054353].
Synemosyna formica Peckham & Peckham, 1883: 30, pl. 3, f. 23 (f, Dm).
Synemosyna formica Peckham & Peckham, 1888: 93, pl. 6, f. 70 (mf, S of Janus gibberosus).
Synemosyna formica Emerton, 1891: 243, pl. 21, f. 5 (mf).
Synemosyna formica Peckham & Peckham, 1892: 77, pl. 6, f. 4 (mf).
Synemosyna formica Simon, 1901a: 512, f. 612 (m).
Synemosyna formica Emerton, 1902: 64, f. 163-164 (mf).
Synemosyna formica Peckham & Peckham, 1909: 366, pl. 50, f. 1 (mf).
Synemosyna formica Comstock, 1912: 672, f. 743-744, 747.
Myrmecium rubrum Mello-Leitão, 1932b: 150 (possible senior S, see Synemosyna rubra).
Synemosyna lunata Chamberlin & Ivie, 1944: 215 (possible senior S, see Synemosyna lunata).
Synemosyna formica Chickering, 1944: 208, f. 136-139 (mf).
Synemosyna formica Kaston, 1948: 448, f. 1609-1610, 1623-24 (mf).
Synemosyna formica Galiano, 1966a: 357, f. 1-4, 36-37, 50-51, 62 (mf).
Synemosyna formica Oehler, 1980: 5, f. 1-4 (m).
Synemosyna formica Prószyński, 2017b: 61, f. 27D (mf).

Synemosyna hentzii Peckham & Peckham, 1892: 78, pl. 7, f. 2 (Df).

Synemosyna invemar Cutler & Müller, 1991: 174, f. 9-12 (Df).

Synemosyna maddisoni Cutler, 1985: 89, f. 19-22 (Df).
Synemosyna maddisoni Cutler, 1988b: 199, f. 1-2, 5-6 (Dm).
Synemosyna maddisoni Chamé-Vázquez, Cutler & Ibarra-Núñez, 2020: 477, f. 1-19 (mf).

Janus myrmeciaeformis Taczanowski, 1871: 125, pl. 4, f. 9 (Dm).
Simonella myrmeciaeformis Peckham, Peckham & Wheeler, 1889: 253, pl. 12, f. 8 (m, T from Janus).
Simonella myrmeciaeformis Peckham & Peckham, 1892: 81, pl. 7, f. 4 (m, Df).
Simonella myrmeciaeformis Simon, 1901a: 509, f. 605-609 (m).
Simonella peckhami Mello-Leitão, 1933a: 56 (nomen novum for Simonella myrmeciaeformis sensu Peckham & Peckham, 1892) [urn:lsid:nmbe.ch:spidersp:055592].
Synemosyna myrmeciformis Galiano, 1966a: 367, f. 18-20, 38-39 (m, T from Simonella, S of Simonella peckhami).
Synemosyna myrmeciaeformis Perger, Rubio & Haddad, 2021: 74, f. 3B, E, 4B, E, 5A-B, 8A-D (f).

Synemosyna nicaraguaensis Cutler, 1993: 2, f. 1-2 (Df).
Synemosyna nicaraguaensis Perger, Rubio & Haddad, 2021: 76, f. 3C, F, 4C, F, 5C-F, 9A-D (Dm, f).

Synemosyna paraensis Galiano, 1967a: 38, f. 25-28 (Dm).
Synemosyna paraensis Galiano, 1971c: 133, f. 1-3 (Df).
Synemosyna paraensis Carvalho & Gasnier, 2019: CB41, f. 187-188 (f).

Simonella petrunkevitchi Chapin, 1922: 129, f. 1-2 (Dm).
Synemosyna petrunkevitchi Galiano, 1966a: 370, f. 15-17, 40-41 (m).
Synemosyna petrunkevitchi Cala-Riquelme, 2010: 85, f. 1A-B (m).

Simonella scutata Mello-Leitão, 1943a: 231, f. 58 (Df).
Synemosyna scutata Galiano, 1966a: 371, f. 59 (f).

Synemosyna smithi Peckham & Peckham, 1894b: 692, pl. 61, f. 1 (Dmf).
Synemosyna smithi Banks, 1926: 427, pl. 93, f. 5-6 (mf).
Synemosyna smithi Bryant, 1940: 450, f. 244, 246 (m).
Synemosyna smithi Galiano, 1966a: 372, f. 27-32, 54, 56 (mf).

Simonella taperae Mello-Leitão, 1933a: 61, pl. 1, f. 5 (Dm).

Synemosyna ubicki Cutler, 1988b: 200, f. 3-4, 7-10 (Dmf).
Synemosyna ubicki Chamé-Vázquez, Cutler & Ibarra-Núñez, 2020: 478, f. 20-22 (m).